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Trigonometry<br />
4<br />
4.1 Radian and Degree Measure<br />
4.2 Trigonometric Functions: The Unit Circle<br />
4.3 Right Triangle Trigonometry<br />
4.4 Trigonometric Functions of Any Angle<br />
4.5 Graphs of Sine and Cosine Functions<br />
4.6 Graphs of Other Trigonometric Functions<br />
4.7 Inverse Trigonometric Functions<br />
4.8 Applications and Models<br />
In Mathematics<br />
Trigonometry is used to find relationships<br />
between the sides and angles of triangles,<br />
and to write trigonometric functions as<br />
models of real-life quantities.<br />
In Real Life<br />
Trigonometric functions are used to model<br />
quantities that are periodic. For instance,<br />
throughout the day, the depth of water at<br />
the end of a dock in Bar Harbor, Maine<br />
varies with the tides. The depth can be<br />
modeled by a trigonometric function.<br />
(See Example 7, page 325.)<br />
Andre Jenny/Alamy<br />
IN CAREERS<br />
There are many careers that use trigonometry. Several are listed below.<br />
• Biologist<br />
Exercise 70, page 308<br />
• Meteorologist<br />
Exercise 99, page 318<br />
• Mechanical Engineer<br />
Exercise 95, page 339<br />
• Surveyor<br />
Exercise 41, page 359<br />
279
280 Chapter 4 Trigonometry<br />
4.1 RADIAN AND DEGREE MEASURE<br />
What you should learn<br />
• Describe angles.<br />
• Use radian measure.<br />
• Use degree measure.<br />
• Use angles to model and solve<br />
real-life problems.<br />
Why you should learn it<br />
You can use angles to model and solve<br />
real-life problems. For instance, in<br />
Exercise 119 on page 291, you are<br />
asked to use angles to find the speed<br />
of a bicycle.<br />
Angles<br />
As derived from the Greek language, the word trigonometry means “measurement of<br />
triangles.” Initially, trigonometry dealt with relationships among the sides and angles of<br />
triangles and was used in the development of astronomy, navigation, and surveying.<br />
With the development of calculus and the physical sciences in the 17th century, a<br />
different perspective arose—one that viewed the classic trigonometric relationships as<br />
functions with the set of real numbers as their domains. Consequently, the applications<br />
of trigonometry expanded to include a vast number of physical phenomena involving<br />
rotations and vibrations. These phenomena include sound waves, light rays, planetary<br />
orbits, vibrating strings, pendulums, and orbits of atomic particles.<br />
The approach in <strong>this</strong> text incorporates both perspectives, starting with angles and<br />
their measure.<br />
Terminal side<br />
Terminal<br />
side<br />
y<br />
Vertex<br />
Initial side<br />
Initial side<br />
x<br />
© Wolfgang Rattay/Reuters/Corbis<br />
Angle<br />
Angle in standard position<br />
FIGURE 4.1 FIGURE 4.2<br />
An angle is determined by rotating a ray (half-line) about its endpoint. The starting<br />
position of the ray is the initial side of the angle, and the position after rotation is the<br />
terminal side, as shown in Figure 4.1. The endpoint of the ray is the vertex of the<br />
angle. This perception of an angle fits a coordinate system in which the origin is the<br />
vertex and the initial side coincides with the positive x-axis. Such an angle is in<br />
standard position, as shown in Figure 4.2. Positive angles are generated by counterclockwise<br />
rotation, and negative angles by clockwise rotation, as shown in Figure 4.3.<br />
Angles are labeled with Greek letters (alpha), (beta), and (theta), as well as uppercase<br />
letters A, B, and C. In Figure 4.4, note that angles and have the same<br />
initial and terminal sides. Such angles are coterminal.<br />
<br />
<br />
<br />
<br />
<br />
y<br />
y<br />
y<br />
Positive angle<br />
(counterclockwise)<br />
x<br />
Negative angle<br />
(clockwise)<br />
α<br />
β<br />
x<br />
β<br />
α<br />
x<br />
FIGURE 4.3 FIGURE 4.4 Coterminal angles
Section 4.1 Radian and Degree Measure 281<br />
y<br />
s = r<br />
r<br />
θ<br />
x<br />
r<br />
Arc length radius when 1 radian<br />
FIGURE 4.5<br />
<br />
Radian Measure<br />
The measure of an angle is determined by the amount of rotation from the initial side<br />
to the terminal side. One way to measure angles is in radians. This type of measure is<br />
especially useful in calculus. To define a radian, you can use a central angle of a<br />
circle, one whose vertex is the center of the circle, as shown in Figure 4.5.<br />
Definition of Radian<br />
One radian is the measure of a central angle that intercepts an arc s equal in<br />
length to the radius r of the circle. See Figure 4.5. Algebraically, <strong>this</strong> means that<br />
s r<br />
<br />
where<br />
<br />
is measured in radians.<br />
y<br />
Because the circumference of a circle is 2r units, it follows that a central angle<br />
of one full revolution (counterclockwise) corresponds to an arc length of<br />
3<br />
radians<br />
2 radians<br />
r<br />
4 radians<br />
FIGURE 4.6<br />
r<br />
r<br />
r<br />
1 radian<br />
r<br />
r<br />
5 radians<br />
6<br />
radians<br />
x<br />
s 2r.<br />
Moreover, because<br />
there are just over six radius lengths in a full circle, as<br />
shown in Figure 4.6. Because the units of measure for s and r are the same, the ratio sr<br />
has no units—it is simply a real number.<br />
Because the radian measure of an angle of one full revolution is 2, you can obtain<br />
the following.<br />
1<br />
revolution 2 radians<br />
2 <br />
2<br />
1<br />
4<br />
revolution<br />
2 6.28,<br />
<br />
2 radians<br />
4 2<br />
1<br />
6<br />
revolution<br />
<br />
2 radians<br />
6 3<br />
These and other common angles are shown in Figure 4.7.<br />
One revolution around a circle<br />
of radius r corresponds to an<br />
angle of radians because<br />
2<br />
s r 2r<br />
r<br />
2 radians.<br />
π<br />
6<br />
π<br />
4<br />
π<br />
3<br />
π<br />
2<br />
π<br />
2π<br />
FIGURE 4.7<br />
Recall that the four quadrants in a coordinate system are numbered I, II, III, and<br />
IV. Figure 4.8 on page 282 shows which angles between 0 and lie in each of the four<br />
quadrants. Note that angles between 0 and 2 are acute angles and angles between<br />
2 and are obtuse angles.<br />
<br />
2
282 Chapter 4 Trigonometry<br />
θ =<br />
π<br />
2<br />
Quadrant II<br />
π<br />
< θ < π<br />
2<br />
Quadrant I<br />
0 < θ <<br />
π<br />
2<br />
θ = π<br />
θ = 0<br />
Quadrant III Quadrant IV<br />
π < θ <<br />
3π<br />
3π<br />
< θ < 2π<br />
2 2<br />
The phrase “the terminal side<br />
of lies in a quadrant” is often<br />
abbreviated by simply saying<br />
that “ lies in a quadrant.” The<br />
terminal sides of the “quadrant<br />
angles” 0, 2, , and 32 do<br />
not lie within quadrants.<br />
<br />
<br />
FIGURE 4.8<br />
Two angles are coterminal if they have the same initial and terminal sides. For<br />
instance, the angles 0 and are coterminal, as are the angles 6 and 136. You can<br />
find an angle that is coterminal to a given angle by adding or subtracting (one<br />
revolution), as demonstrated in Example 1. A given angle has infinitely many<br />
coterminal angles. For instance, is coterminal with<br />
<br />
6 2n<br />
where n is an integer.<br />
2<br />
6<br />
θ =<br />
3 π 2<br />
<br />
<br />
2<br />
You can review operations<br />
involving fractions in Appendix<br />
A.1.<br />
Example 1<br />
Sketching and Finding Coterminal Angles<br />
a. For the positive angle 136, subtract 2 to obtain a coterminal angle<br />
See Figure 4.9.<br />
6 2 <br />
6 .<br />
13<br />
b. For the positive angle 34, subtract 2 to obtain a coterminal angle<br />
See Figure 4.10.<br />
4 2 5<br />
4 .<br />
3<br />
<br />
c. For the negative angle 23, add 2 to obtain a coterminal angle<br />
2<br />
See Figure 4.11.<br />
3 2 4<br />
3 .<br />
π<br />
π<br />
2<br />
θ = 13 π<br />
6 6<br />
π<br />
3π<br />
2<br />
0<br />
π<br />
FIGURE 4.9 FIGURE 4.10 FIGURE 4.11<br />
Now try Exercise 27.<br />
π<br />
2<br />
3π<br />
2<br />
θ =<br />
3π<br />
4<br />
−<br />
5π<br />
4<br />
0<br />
π<br />
4π<br />
3<br />
π<br />
2<br />
θ = −<br />
2π<br />
3<br />
3π<br />
2<br />
0
Section 4.1 Radian and Degree Measure 283<br />
<br />
<br />
Two positive angles and are complementary (complements of each other) if<br />
their sum is 2. Two positive angles are supplementary (supplements of each other)<br />
if their sum is . See Figure 4.12.<br />
β<br />
α<br />
β<br />
α<br />
Complementary angles<br />
FIGURE 4.12<br />
Supplementary angles<br />
Example 2<br />
Complementary and Supplementary Angles<br />
If possible, find the complement and the supplement of (a) 25 and (b) 45.<br />
Solution<br />
a. The complement of 25 is<br />
<br />
2 2<br />
5 5<br />
10 4<br />
10 10 .<br />
The supplement of 25 is<br />
2<br />
b. Because 45 is greater than 2, it has no complement. (Remember that complements<br />
are positive angles.) The supplement is<br />
4<br />
<br />
5 5<br />
5 2<br />
5 3<br />
5 .<br />
<br />
5 5<br />
5 4<br />
5 5 .<br />
Now try Exercise 31.<br />
120°<br />
135°<br />
150°<br />
180°<br />
1<br />
90 ° = (360 ° ) 4<br />
1<br />
60°= (360 ° )<br />
6<br />
1<br />
45°= (360 ° )<br />
8<br />
1<br />
30°= (360 ° )<br />
12<br />
θ 0°<br />
360°<br />
210°<br />
330°<br />
225° 315°<br />
240° 270° 300°<br />
FIGURE 4.13<br />
y<br />
x<br />
Degree Measure<br />
A second way to measure angles is in terms of degrees, denoted by the symbol .<br />
1<br />
A measure of one degree (1 ) is equivalent to a rotation of 360 of a complete revolution<br />
about the vertex. To measure angles, it is convenient to mark degrees on the<br />
circumference of a circle, as shown in Figure 4.13. So, a full revolution (counterclockwise)<br />
corresponds to 360, a half revolution to 180, a quarter revolution to 90, and<br />
so on.<br />
Because radians corresponds to one complete revolution, degrees and radians<br />
are related by the equations<br />
360 2 rad and 180 rad.<br />
From the latter equation, you obtain<br />
180<br />
1 <br />
and 1 rad <br />
180 rad <br />
<br />
2<br />
which lead to the conversion rules at the top of the next page.
284 Chapter 4 Trigonometry<br />
Conversions Between Degrees and Radians<br />
rad<br />
1. To convert degrees to radians, multiply degrees by<br />
180 .<br />
180<br />
2. To convert radians to degrees, multiply radians by<br />
rad .<br />
To apply these two conversion rules, use the basic relationship<br />
(See Figure 4.14.)<br />
rad 180.<br />
π<br />
6<br />
π<br />
4<br />
30° 45°<br />
π<br />
3<br />
60°<br />
π<br />
2<br />
90°<br />
FIGURE 4.14<br />
π<br />
180°<br />
2π<br />
360°<br />
When no units of angle measure are specified, radian measure is implied. For<br />
instance, if you write you imply that radians.<br />
2,<br />
2<br />
Example 3<br />
Converting from Degrees to Radians<br />
TECHNOLOGY<br />
With calculators it is convenient<br />
to use decimal degrees to denote<br />
fractional parts of degrees.<br />
Historically, however, fractional<br />
parts of degrees were expressed<br />
in minutes and seconds, using<br />
the prime ( ) and double prime<br />
( ) notations, respectively. That is,<br />
<br />
<br />
1 one minute 1 601<br />
1 one second 1<br />
Consequently, an angle of<br />
64 degrees, 32 minutes, and<br />
47 seconds is represented by<br />
Many calculators<br />
have special keys for converting<br />
an angle in degrees, minutes,<br />
and seconds D M S to decimal<br />
degree form, and vice versa.<br />
64 32 47.<br />
36001.<br />
a. 135 135 deg <br />
Multiply by 180.<br />
180 deg 3<br />
4 radians<br />
b. 540 540 deg <br />
Multiply by 180.<br />
c. 270 270 deg <br />
Multiply by 180.<br />
180 deg 3<br />
2 radians<br />
Example 4<br />
Now try Exercise 57.<br />
Converting from Radians to Degrees<br />
a. <br />
2 rad 2 rad 180 deg<br />
Multiply by<br />
b.<br />
2 rad 9<br />
2 rad 180 deg<br />
Multiply by 180.<br />
9<br />
<br />
<br />
rad<br />
rad<br />
180 deg 3 radians<br />
rad<br />
rad 90<br />
rad 810 180.<br />
c. 2 rad 2 rad <br />
180 deg<br />
114.59<br />
Multiply by 180.<br />
rad 360<br />
<br />
Now try Exercise 61.<br />
If you have a calculator with a “radian-to-degree” conversion key, try using it to<br />
verify the result shown in part (b) of Example 4.
Section 4.1 Radian and Degree Measure 285<br />
Applications<br />
The radian measure formula,<br />
sr,<br />
can be used to measure arc length along a circle.<br />
s<br />
θ = 240°<br />
r = 4<br />
Arc Length<br />
For a circle of radius r, a central angle intercepts an arc of length s given by<br />
s r Length of circular arc<br />
<br />
where is measured in radians. Note that if r 1, then s , and the radian<br />
measure of equals the arc length.<br />
<br />
<br />
Example 5<br />
Finding Arc Length<br />
FIGURE 4.15<br />
A circle has a radius of 4 inches. Find the length of the arc intercepted by a central angle<br />
of 240, as shown in Figure 4.15.<br />
Solution<br />
To use the formula s r, first convert 240 to radian measure.<br />
240 240 deg 180 deg<br />
Then, using a radius of r 4 inches, you can find the arc length to be<br />
s r<br />
4<br />
3 radians<br />
4 <br />
4<br />
3 <br />
16 16.76 inches.<br />
3<br />
r<br />
rad<br />
Note that the units for are determined by the units for r because is given in radian<br />
measure, which has no units.<br />
Now try Exercise 89.<br />
<br />
Linear speed measures how fast<br />
the particle moves, and angular<br />
speed measures how fast the<br />
angle changes. By dividing the<br />
formula for arc length by t,<br />
you can establish a relationship<br />
between linear speed v and<br />
angular speed , as shown.<br />
s r<br />
s<br />
t r<br />
t<br />
v r<br />
The formula for the length of a circular arc can be used to analyze the motion of a<br />
particle moving at a constant speed along a circular path.<br />
Linear and Angular Speeds<br />
Consider a particle moving at a constant speed along a circular arc of radius r. If s<br />
is the length of the arc traveled in time t, then the linear speed v of the particle is<br />
Linear speed v <br />
<br />
Moreover, if is the angle (in radian measure) corresponding to the arc length s,<br />
then the angular speed (the lowercase Greek letter omega) of the particle is<br />
Angular speed <br />
arc length<br />
time<br />
<br />
s t .<br />
central angle<br />
time<br />
<br />
<br />
t .
286 Chapter 4 Trigonometry<br />
Example 6<br />
Finding Linear Speed<br />
FIGURE 4.16<br />
10.2 cm<br />
The second hand of a clock is 10.2 centimeters long, as shown in Figure 4.16. Find the<br />
linear speed of the tip of <strong>this</strong> second hand as it passes around the clock face.<br />
Solution<br />
In one revolution, the arc length traveled is<br />
s 2r<br />
210.2<br />
20.4 centimeters.<br />
Substitute for r.<br />
The time required for the second hand to travel <strong>this</strong> distance is<br />
t 1 minute 60 seconds.<br />
So, the linear speed of the tip of the second hand is<br />
116 ft<br />
Linear speed s t<br />
20.4 centimeters<br />
60 seconds<br />
1.068 centimeters per second.<br />
Now try Exercise 111.<br />
Example 7<br />
Finding Angular and Linear Speeds<br />
The blades of a wind turbine are 116 feet long (see Figure 4.17). The propeller rotates<br />
at 15 revolutions per minute.<br />
a. Find the angular speed of the propeller in radians per minute.<br />
b. Find the linear speed of the tips of the blades.<br />
FIGURE 4.17<br />
Solution<br />
a. Because each revolution generates radians, it follows that the propeller turns<br />
152 30 radians per minute. In other words, the angular speed is<br />
Angular speed <br />
t<br />
b. The linear speed is<br />
<br />
30 radians<br />
1 minute<br />
2<br />
30 radians per minute.<br />
Linear speed s t<br />
r<br />
t<br />
11630 feet<br />
1 minute<br />
Now try Exercise 113.<br />
10,933 feet per minute.
Section 4.1 Radian and Degree Measure 287<br />
A sector of a circle is the region bounded by two radii of the circle and their<br />
intercepted arc (see Figure 4.18).<br />
θ<br />
r<br />
FIGURE 4.18<br />
Area of a Sector of a Circle<br />
For a circle of radius r, the area A of a sector of the circle with central angle is<br />
given by<br />
where<br />
A 1 2 r2<br />
<br />
is measured in radians.<br />
<br />
Example 8<br />
Area of a Sector of a Circle<br />
A sprinkler on a golf course fairway sprays water over a distance of 70 feet and rotates<br />
through an angle of 120 (see Figure 4.19). Find the area of the fairway watered by the<br />
sprinkler.<br />
Solution<br />
First convert 120 to radian measure as follows.<br />
FIGURE 4.19<br />
120°<br />
70 ft<br />
120<br />
120 deg 180 deg<br />
2<br />
3 radians<br />
rad<br />
Multiply by 180.<br />
23<br />
Then, using and r 70, the area is<br />
A 1 2 r2<br />
Formula for the area of a sector of a circle<br />
1 2 702 2<br />
3 <br />
4900<br />
3<br />
5131 square feet.<br />
Now try Exercise 117.<br />
Substitute for r and .<br />
Simplify.<br />
Simplify.
288 Chapter 4 Trigonometry<br />
4.1<br />
EXERCISES<br />
VOCABULARY: Fill in the blanks.<br />
1. ________ means “measurement of triangles.”<br />
2. An ________ is determined by rotating a ray about its endpoint.<br />
3. Two angles that have the same initial and terminal sides are ________.<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
4. One ________ is the measure of a central angle that intercepts an arc equal to the radius of the circle.<br />
5. Angles that measure between 0 and 2 are ________ angles, and angles that measure between 2 and<br />
are ________ angles.<br />
6. Two positive angles that have a sum of 2 are ________ angles, whereas two positive angles that have a sum<br />
of are ________ angles.<br />
<br />
7. The angle measure that is equivalent to a rotation of 360 of a complete revolution about an angle’s vertex is<br />
one ________.<br />
8. 180 degrees ________ radians.<br />
9. The ________ speed of a particle is the ratio of arc length to time traveled, and the ________ speed of a particle<br />
is the ratio of central angle to time traveled.<br />
10. The area A of a sector of a circle with radius r and central angle , where is measured in radians, is given by<br />
the formula ________.<br />
SKILLS AND APPLICATIONS<br />
1<br />
<br />
<br />
In Exercises 11–16, estimate the angle to the nearest one-half<br />
radian.<br />
11. 12.<br />
11<br />
25. (a) (b)<br />
6<br />
26. (a) 4 (b)<br />
3<br />
7<br />
13. 14.<br />
In Exercises 27–30, determine two coterminal angles (one<br />
positive and one negative) for each angle. Give your answers<br />
in radians.<br />
27. (a) π<br />
(b)<br />
2<br />
π<br />
θ = π 6<br />
0<br />
π<br />
π<br />
2<br />
5<br />
θ = π 6<br />
0<br />
15. 16.<br />
In Exercises 17–22, determine the quadrant in which each<br />
angle lies. (The angle measure is given in radians.)<br />
<br />
17. (a) (b) 18. (a) (b)<br />
4 4<br />
8<br />
19. (a) (b) 20. (a) 5 (b)<br />
6 3<br />
6<br />
21. (a) 3.5 (b) 2.25 22. (a) 6.02 (b)<br />
In Exercises 23–26, sketch each angle in standard position.<br />
<br />
<br />
5<br />
<br />
11<br />
23. (a) (b) 2 24. (a) 7 (b)<br />
3<br />
3<br />
4<br />
9<br />
8<br />
11<br />
9<br />
4.25<br />
5<br />
2<br />
28. (a) π<br />
(b)<br />
2<br />
7<br />
θ = π 6<br />
π<br />
3π<br />
2<br />
3π<br />
2<br />
2<br />
29. (a) (b)<br />
3<br />
9<br />
30. (a) (b)<br />
4<br />
0<br />
π<br />
3π<br />
2<br />
<br />
<br />
12<br />
π<br />
2<br />
3π<br />
2<br />
2<br />
15<br />
0<br />
θ = −<br />
11π<br />
6
Section 4.1 Radian and Degree Measure 289<br />
In Exercises 31–34, find (if possible) the complement and<br />
supplement of each angle.<br />
31. (a) 3 (b) 4 32. (a) 12 (b) 1112<br />
33. (a) 1 (b) 2 34. (a) 3 (b) 1.5<br />
In Exercises 35–40, estimate the number of degrees in the<br />
angle. Use a protractor to check your answer.<br />
35. 36.<br />
37. 38.<br />
39. 40.<br />
In Exercises 41–44, determine the quadrant in which each<br />
angle lies.<br />
41. (a) 130<br />
(b) 285<br />
42. (a) 8.3<br />
(b) 257 30<br />
43. (a) 132 50 (b) 336<br />
44. (a) 260<br />
(b) 3.4<br />
In Exercises 45–48, sketch each angle in standard position.<br />
45. (a) 90 (b) 180 46. (a) 270 (b) 120<br />
47. (a) 30 (b) 135<br />
48. (a) 750 (b) 600<br />
In Exercises 49–52, determine two coterminal angles (one<br />
positive and one negative) for each angle. Give your answers<br />
in degrees.<br />
49. (a) 90° (b)<br />
θ = 45°<br />
180°<br />
50. (a) (b)<br />
180°<br />
240<br />
270°<br />
90°<br />
270°<br />
51. (a) (b)<br />
0<br />
θ = 120°<br />
0<br />
180°<br />
θ = −420°<br />
180°<br />
90°<br />
90°<br />
270°<br />
180<br />
0<br />
θ = −36°<br />
270°<br />
0<br />
52. (a) (b)<br />
In Exercises 53–56, find (if possible) the complement and<br />
supplement of each angle.<br />
53. (a) 18 (b) 85 54. (a) 46 (b) 93<br />
55. (a) 150 (b) 79 56. (a) 130 (b) 170<br />
In Exercises 57–60, rewrite each angle in radian measure as a<br />
multiple of . (Do not use a calculator.)<br />
57. (a) 30 (b) 45 58. (a) 315 (b) 120<br />
59. (a) 20 (b) 60 60. (a) 270 (b) 144<br />
In Exercises 61–64, rewrite each angle in degree measure.<br />
(Do not use a calculator.)<br />
3<br />
61. (a) (b) 62. (a) 7 (b)<br />
2<br />
6<br />
12 9<br />
5<br />
63. (a) (b) 7 64. (a) (b)<br />
4<br />
3<br />
6<br />
In Exercises 65–72, convert the angle measure from degrees<br />
to radians. Round to three decimal places.<br />
65. 45<br />
66. 87.4<br />
67. 216.35<br />
68. 48.27<br />
69. 532<br />
70. 345<br />
71. 0.83<br />
72. 0.54<br />
In Exercises 73–80, convert the angle measure from radians<br />
to degrees. Round to three decimal places.<br />
73. 7<br />
74. 511<br />
75. 158<br />
76. 132<br />
77. 78.<br />
4.2<br />
390<br />
7<br />
79. 2<br />
80. 0.57<br />
In Exercises 81–84, convert each angle measure to decimal<br />
degree form without using a calculator. Then check your<br />
answers using a calculator.<br />
81. (a) 54 45 (b) 128 30<br />
82. (a) 245 10 (b) 2 12<br />
83. (a) 85 18 30 (b) 330 25<br />
84. (a) 135 36 (b) 408 16 20<br />
In Exercises 85–88, convert each angle measure to degrees,<br />
minutes, and seconds without using a calculator. Then check<br />
your answers using a calculator.<br />
85. (a) 240.6 (b) 145.8<br />
86. (a) 345.12 (b) 0.45<br />
87. (a) 2.5 (b) 3.58<br />
88. (a) 0.36 (b) 0.79<br />
230<br />
4.8<br />
11<br />
<br />
34<br />
15
290 Chapter 4 Trigonometry<br />
In Exercises 89–92, find the length of the arc on a circle of<br />
radius r intercepted by a central angle .<br />
Radius r<br />
89. 15 inches<br />
90. 9 feet<br />
91. 3 meters<br />
92. 20 centimeters<br />
Central Angle<br />
In Exercises 93–96, find the radian measure of the central<br />
angle of a circle of radius r that intercepts an arc of length s.<br />
Radius r<br />
Arc Length s<br />
93. 4 inches 18 inches<br />
94. 14 feet 8 feet<br />
95. 25 centimeters 10.5 centimeters<br />
96. 80 kilometers 150 kilometers<br />
In Exercises 97–100, use the given arc length and radius to<br />
find the angle (in radians).<br />
<br />
120<br />
60<br />
150<br />
45<br />
97. 98.<br />
25<br />
θ<br />
1<br />
θ<br />
2<br />
10<br />
<br />
City<br />
106. San Francisco, California<br />
Seattle, Washington<br />
Latitude<br />
37 47 36 N<br />
47 37 18 N<br />
107. DIFFERENCE IN LATITUDES Assuming that Earth<br />
is a sphere of radius 6378 kilometers, what is the<br />
difference in the latitudes of Syracuse, New York<br />
and Annapolis, Maryland, where Syracuse is about<br />
450 kilometers due north of Annapolis?<br />
108. DIFFERENCE IN LATITUDES Assuming that Earth<br />
is a sphere of radius 6378 kilometers, what is the<br />
difference in the latitudes of Lynchburg, Virginia and<br />
Myrtle Beach, South Carolina, where Lynchburg is<br />
about 400 kilometers due north of Myrtle Beach?<br />
109. INSTRUMENTATION The pointer on a voltmeter is<br />
6 centimeters in length (see figure). Find the angle<br />
through which the pointer rotates when it moves<br />
2.5 centimeters on the scale.<br />
10 in.<br />
99. 28<br />
100.<br />
θ<br />
In Exercises 101–104, find the area of the sector of the circle<br />
with radius r and central angle .<br />
Radius r<br />
101. 6 inches<br />
102. 12 millimeters<br />
103. 2.5 feet<br />
104. 1.4 miles<br />
Central Angle<br />
DISTANCE BETWEEN CITIES In Exercises 105 and 106,<br />
find the distance between the cities. Assume that Earth is a<br />
sphere of radius 4000 miles and that the cities are on the<br />
same longitude (one city is due north of the other).<br />
City<br />
7<br />
105. Dallas, Texas<br />
Omaha, Nebraska<br />
3<br />
4<br />
225<br />
330<br />
<br />
Latitude<br />
75<br />
θ<br />
32 47 39 N<br />
41 15 50 N<br />
60<br />
6 cm<br />
FIGURE FOR 109 FIGURE FOR 110<br />
110. ELECTRIC HOIST An electric hoist is being used to<br />
lift a beam (see figure). The diameter of the drum on<br />
the hoist is 10 inches, and the beam must be raised<br />
2 feet. Find the number of degrees through which the<br />
drum must rotate.<br />
111. LINEAR AND ANGULAR SPEEDS A circular power<br />
saw has a inch-diameter blade that rotates at<br />
5000 revolutions per minute.<br />
7 1 4 - 2 ft<br />
Not drawn to scale<br />
(a) Find the angular speed of the saw blade in radians<br />
per minute.<br />
(b) Find the linear speed (in feet per minute) of one of<br />
the 24 cutting teeth as they contact the wood being<br />
cut.<br />
112. LINEAR AND ANGULAR SPEEDS A carousel with<br />
a 50-foot diameter makes 4 revolutions per minute.<br />
(a) Find the angular speed of the carousel in radians<br />
per minute.<br />
(b) Find the linear speed (in feet per minute) of the<br />
platform rim of the carousel.
Section 4.1 Radian and Degree Measure 291<br />
113. LINEAR AND ANGULAR SPEEDS The diameter of<br />
a DVD is approximately 12 centimeters. The drive<br />
motor of the DVD player is controlled to rotate<br />
precisely between 200 and 500 revolutions per minute,<br />
depending on what track is being read.<br />
(a) Find an interval for the angular speed of a DVD as<br />
it rotates.<br />
(b) Find an interval for the linear speed of a point on<br />
the outermost track as the DVD rotates.<br />
114. ANGULAR SPEED A two-inch-diameter pulley on<br />
an electric motor that runs at 1700 revolutions per<br />
minute is connected by a belt to a four-inch-diameter<br />
pulley on a saw arbor.<br />
(a) Find the angular speed (in radians per minute) of<br />
each pulley.<br />
(b) Find the revolutions per minute of the saw.<br />
115. ANGULAR SPEED A car is moving at a rate of<br />
65 miles per hour, and the diameter of its wheels is 2 feet.<br />
(a) Find the number of revolutions per minute the<br />
wheels are rotating.<br />
(b) Find the angular speed of the wheels in radians per<br />
minute.<br />
116. ANGULAR SPEED A computerized spin balance<br />
machine rotates a 25-inch-diameter tire at 480 revolutions<br />
per minute.<br />
(a) Find the road speed (in miles per hour) at which<br />
the tire is being balanced.<br />
(b) At what rate should the spin balance machine be set<br />
so that the tire is being tested for 55 miles per hour?<br />
117. AREA A sprinkler on a golf green is set to spray<br />
water over a distance of 15 meters and to rotate through<br />
an angle of 140. Draw a diagram that shows the region<br />
that can be irrigated with the sprinkler. Find the area of<br />
the region.<br />
118. AREA A car’s rear windshield wiper rotates 125.<br />
The total length of the wiper mechanism is 25 inches<br />
and wipes the windshield over a distance of 14 inches.<br />
Find the area covered by the wiper.<br />
119. SPEED OF A BICYCLE The radii of the pedal<br />
sprocket, the wheel sprocket, and the wheel of the<br />
bicycle in the figure are 4 inches, 2 inches, and<br />
14 inches, respectively. A cyclist is pedaling at a rate<br />
of 1 revolution per second.<br />
14 in.<br />
2 in.<br />
4 in.<br />
(a) Find the speed of the bicycle in feet per second and<br />
miles per hour.<br />
(b) Use your result from part (a) to write a function<br />
for the distance d (in miles) a cyclist travels in<br />
terms of the number n of revolutions of the pedal<br />
sprocket.<br />
(c) Write a function for the distance d (in miles) a<br />
cyclist travels in terms of the time t (in seconds).<br />
Compare <strong>this</strong> function with the function from<br />
part (b).<br />
(d) Classify the types of functions you found in parts<br />
(b) and (c). Explain your reasoning.<br />
120. CAPSTONE Write a short paper in your own words<br />
explaining the meaning of each of the following<br />
concepts to a classmate.<br />
(a) an angle in standard position<br />
(b) positive and negative angles<br />
(c) coterminal angles<br />
(d) angle measure in degrees and radians<br />
(e) obtuse and acute angles<br />
(f) complementary and supplementary angles<br />
EXPLORATION<br />
TRUE OR FALSE? In Exercises 121–123, determine<br />
whether the statement is true or false. Justify your answer.<br />
121. A measurement of 4 radians corresponds to two<br />
complete revolutions from the initial side to the<br />
terminal side of an angle.<br />
122. The difference between the measures of two<br />
coterminal angles is always a multiple of 360 if<br />
expressed in degrees and is always a multiple of<br />
radians if expressed in radians.<br />
123. An angle that measures 1260 lies in Quadrant III.<br />
124. THINK ABOUT IT A fan motor turns at a given<br />
angular speed. How does the speed of the tips of the<br />
blades change if a fan of greater diameter is installed<br />
on the motor? Explain.<br />
125. THINK ABOUT IT Is a degree or a radian the larger<br />
unit of measure? Explain.<br />
126. WRITING If the radius of a circle is increasing and<br />
the magnitude of a central angle is held constant, how<br />
is the length of the intercepted arc changing? Explain<br />
your reasoning.<br />
127. <strong>PRO</strong>OF Prove that the area of a circular sector of<br />
radius r with central angle is A 1 2r 2 , where is<br />
measured in radians.<br />
<br />
<br />
2
292 Chapter 4 Trigonometry<br />
4.2 TRIGONOMETRIC FUNCTIONS: THE UNIT CIRCLE<br />
What you should learn<br />
• Identify a unit circle and describe<br />
its relationship to real numbers.<br />
• Evaluate trigonometric functions<br />
using the unit circle.<br />
• Use the domain and period to<br />
evaluate sine and cosine functions.<br />
• Use a calculator to evaluate<br />
trigonometric functions.<br />
Why you should learn it<br />
Trigonometric functions are used to<br />
model the movement of an oscillating<br />
weight. For instance, in Exercise 60<br />
on page 298, the displacement from<br />
equilibrium of an oscillating weight<br />
suspended by a spring is modeled as<br />
a function of time.<br />
The Unit Circle<br />
The two historical perspectives of trigonometry incorporate different methods for<br />
introducing the trigonometric functions. Our first introduction to these functions is<br />
based on the unit circle.<br />
Consider the unit circle given by<br />
x 2 y 2 1<br />
as shown in Figure 4.20.<br />
Unit circle<br />
( −1, 0)<br />
(0, 1)<br />
y<br />
(1, 0)<br />
x<br />
FIGURE 4.20<br />
(0, −1)<br />
Richard Megna/Fundamental Photographs<br />
Imagine that the real number line is wrapped around <strong>this</strong> circle, with positive numbers<br />
corresponding to a counterclockwise wrapping and negative numbers corresponding to<br />
a clockwise wrapping, as shown in Figure 4.21.<br />
t > 0<br />
y<br />
( x, y)<br />
t<br />
θ<br />
(1, 0)<br />
t<br />
x<br />
t < 0<br />
y<br />
θ<br />
(1, 0)<br />
x<br />
t<br />
( x, y)<br />
t<br />
FIGURE 4.21<br />
As the real number line is wrapped around the unit circle, each real number t<br />
corresponds to a point x, y on the circle. For example, the real number 0 corresponds<br />
to the point 1, 0. Moreover, because the unit circle has a circumference of 2, the real<br />
number also corresponds to the point 1, 0.<br />
In general, each real number t also corresponds to a central angle (in standard<br />
position) whose radian measure is t. With <strong>this</strong> interpretation of t, the arc length<br />
formula s r (with r 1) indicates that the real number t is the (directional) length<br />
of the arc intercepted by the angle , given in radians.<br />
2
Section 4.2 Trigonometric Functions: The Unit Circle 293<br />
The Trigonometric Functions<br />
From the preceding discussion, it follows that the coordinates x and y are two functions<br />
of the real variable t. You can use these coordinates to define the six trigonometric<br />
functions of t.<br />
sine cosecant cosine secant tangent cotangent<br />
These six functions are normally abbreviated sin, csc, cos, sec, tan, and cot, respectively.<br />
Note in the definition at the<br />
right that the functions in the<br />
second row are the reciprocals<br />
of the corresponding functions<br />
in the first row.<br />
Definitions of Trigonometric Functions<br />
Let t be a real number and let x, y be the point on the unit circle corresponding<br />
to t.<br />
sin t y<br />
cos t x<br />
tan t y x 0<br />
x ,<br />
csc t 1 y 0 sec t 1 x 0 cot t x y 0<br />
y , x ,<br />
y ,<br />
y<br />
(0, 1)<br />
2 2<br />
2<br />
, ,<br />
2 2<br />
2<br />
( − )<br />
2 2<br />
, −<br />
2 2<br />
( −1, 0)<br />
( − )<br />
FIGURE 4.22<br />
1 3<br />
( − , )<br />
2 2<br />
( − )<br />
3 1<br />
,<br />
2 2<br />
( − )<br />
3 1<br />
, −<br />
2 2<br />
1<br />
− , −<br />
2<br />
( −1, 0)<br />
( )<br />
FIGURE 4.23<br />
3<br />
2<br />
(0, −1)<br />
y<br />
(0, 1)<br />
(0, −1)<br />
( )<br />
(1, 0)<br />
2<br />
2<br />
x<br />
( )<br />
2 2<br />
, −<br />
2 2<br />
( )<br />
1<br />
,<br />
2<br />
(1, 0)<br />
3<br />
2<br />
( )<br />
3 1<br />
,<br />
2 2<br />
x<br />
1 3<br />
( , −<br />
2 2 )<br />
( )<br />
3 1<br />
, −<br />
2 2<br />
In the definitions of the trigonometric functions, note that the tangent and secant<br />
are not defined when x 0. For instance, because t 2 corresponds to<br />
x, y 0, 1, it follows that tan2 and sec2 are undefined. Similarly, the<br />
cotangent and cosecant are not defined when y 0. For instance, because t 0<br />
corresponds to x, y 1, 0, cot 0 and csc 0 are undefined.<br />
In Figure 4.22, the unit circle has been divided into eight equal arcs, corresponding<br />
to t-values of<br />
<br />
0,<br />
4 ,<br />
2 , 3<br />
4 , ,<br />
Similarly, in Figure 4.23, the unit circle has been divided into 12 equal arcs,<br />
corresponding to t-values of<br />
<br />
0,<br />
and 2.<br />
6 , 3 , 2 , 2<br />
3 , 5<br />
6 , ,<br />
6 , 3 , 2 , 3 , 6 ,<br />
To verify the points on the unit circle in Figure 4.22, note that 2 also lies<br />
2 , 2<br />
2 <br />
on the line y x. So, substituting x for y in the equation of the unit circle produces<br />
the following.<br />
x 2 x 2 1<br />
5 3 7<br />
4 ,<br />
and 2.<br />
2 , 4 ,<br />
7 4 3 5 11<br />
2x 2 1<br />
x 2 1 2<br />
x ± 2<br />
2<br />
Because the point is in the first quadrant, x 2 and because y x, you also<br />
have y 2<br />
2<br />
You can use similar reasoning to verify the rest of the points in<br />
2 .<br />
Figure 4.22 and the points in Figure 4.23.<br />
Using the x, y coordinates in Figures 4.22 and 4.23, you can evaluate the trigonometric<br />
functions for common t-values. This procedure is demonstrated in Examples 1,<br />
2, and 3. You should study and learn these exact function values for common t-values<br />
because they will help you in later sections to perform calculations.
294 Chapter 4 Trigonometry<br />
Example 1<br />
Evaluating Trigonometric Functions<br />
You can review dividing<br />
fractions and rationalizing<br />
denominators in Appendix A.1<br />
and Appendix A.2, respectively.<br />
Evaluate the six trigonometric functions at each real number.<br />
<br />
a. t b. t 5 c. t 0 d. t <br />
6<br />
4<br />
Solution<br />
For each t-value, begin by finding the corresponding point x, y on the unit circle. Then<br />
use the definitions of trigonometric functions listed on page 293.<br />
<br />
a. t corresponds to the point<br />
6<br />
cos<br />
<br />
sin 6 y 1 2<br />
<br />
6 x 3<br />
2<br />
<br />
tan 6 y x 12<br />
32 <br />
b. t 5 corresponds to the point<br />
4<br />
5<br />
sin<br />
4 y 2 2<br />
5<br />
cos<br />
4 x 2 2<br />
5<br />
tan<br />
4 y x 22<br />
x, y <br />
3<br />
2 , 1 2 .<br />
1<br />
3 3<br />
3<br />
x, y 2<br />
2 , 2 2 .<br />
22 1 sec 5<br />
c. t 0 corresponds to the point x, y 1, 0.<br />
csc<br />
6 1 y 1<br />
12 2<br />
sec<br />
cot<br />
<br />
<br />
6 1 x 2 3 23<br />
3<br />
<br />
6 x y 32<br />
12<br />
3<br />
csc 5<br />
4 1 y 2<br />
2 2<br />
4 1 x 2<br />
2 2<br />
cot 5<br />
4 x y 22<br />
22 1<br />
sin 0 y 0<br />
csc 0 1 is undefined.<br />
y<br />
cos 0 x 1<br />
sec 0 1 x 1 1 1<br />
tan 0 y cot 0 x is undefined.<br />
x 0 1 0 y<br />
d. t corresponds to the point x, y 1, 0.<br />
sin y 0<br />
csc 1 is undefined.<br />
y<br />
cos x 1<br />
sec 1 x 1<br />
1 1<br />
tan y cot x is undefined.<br />
x 0<br />
1 0 y<br />
Now try Exercise 23.
Section 4.2 Trigonometric Functions: The Unit Circle 295<br />
Example 2<br />
Evaluating Trigonometric Functions<br />
Evaluate the six trigonometric functions at t <br />
3 .<br />
Solution<br />
Moving clockwise around the unit circle, it follows that t 3 corresponds to the<br />
point x, y 12, 32.<br />
<br />
sin <br />
3 3 2<br />
<br />
cos 3 1 2<br />
<br />
tan <br />
3 32 3<br />
12<br />
Now try Exercise 33.<br />
csc <br />
3 2<br />
3 23 3<br />
sec <br />
3 2<br />
cot <br />
<br />
<br />
<br />
<br />
3 <br />
12<br />
32 1<br />
3 3 3<br />
y<br />
(0, 1)<br />
(−1, 0) (1, 0)<br />
x −1 ≤ y ≤ 1<br />
(0, −1)<br />
−1 ≤ x ≤ 1<br />
FIGURE 4.24<br />
π π π<br />
t = , + 2π,<br />
+ 4 π, ...<br />
2 2 y 2<br />
3π<br />
3π<br />
π π<br />
t = , + 2π<br />
t = , + 2<br />
4 4 , ...<br />
π, ...<br />
4 4<br />
t = π, 3 π, ...<br />
x<br />
t = 0, 2 π, ...<br />
5π<br />
5π<br />
t =<br />
4 , 4 + 2π, ...<br />
7π<br />
7π<br />
t = 4<br />
, 4<br />
+ 2π, ...<br />
3<br />
t = π 3<br />
2<br />
, π 3<br />
2<br />
+ 2 π,<br />
π<br />
2<br />
+ 4 π, ...<br />
FIGURE 4.25<br />
Domain and Period of Sine and Cosine<br />
The domain of the sine and cosine functions is the set of all real numbers. To determine<br />
the range of these two functions, consider the unit circle shown in Figure 4.24. By<br />
definition, sin t y and cos t x. Because x, y is on the unit circle, you know that<br />
1 y 1 and 1 x 1. So, the values of sine and cosine also range between<br />
1 and 1.<br />
and<br />
Adding to each value of t in the interval 0, 2 completes a second revolution<br />
around the unit circle, as shown in Figure 4.25. The values of sint 2 and<br />
cost 2 correspond to those of sin t and cos t. Similar results can be obtained for<br />
repeated revolutions (positive or negative) on the unit circle. This leads to the general<br />
result<br />
and<br />
1 <br />
1 sin t 1<br />
2<br />
y<br />
1<br />
sint 2n sin t<br />
cost 2 n cos t<br />
1 <br />
1 cos t 1<br />
for any integer n and real number t. Functions that behave in such a repetitive (or cyclic)<br />
manner are called periodic.<br />
Definition of Periodic Function<br />
x<br />
1<br />
A function f is periodic if there exists a positive real number c such that<br />
ft c f t<br />
for all t in the domain of f. The smallest number c for which f is periodic is<br />
called the period of f.
296 Chapter 4 Trigonometry<br />
Recall from Section 1.5 that a function f is even if f t f t, and is odd if<br />
f t f t.<br />
Even and Odd Trigonometric Functions<br />
The cosine and secant functions are even.<br />
cost cos t sect sec t<br />
The sine, cosecant, tangent, and cotangent functions are odd.<br />
sint sin t csct csc t<br />
tant tan t cott cot t<br />
Example 3<br />
Using the Period to Evaluate the Sine and Cosine<br />
From the definition of periodic<br />
function, it follows that the<br />
sine and cosine functions are<br />
periodic and have a period of<br />
2. The other four trigonometric<br />
functions are also periodic, and<br />
will be discussed further in<br />
Section 4.6.<br />
TECHNOLOGY<br />
When evaluating trigonometric<br />
functions with a calculator,<br />
remember to enclose all fractional<br />
angle measures in parentheses.<br />
For instance, if you want to<br />
evaluate sin t for t /6, you<br />
should enter<br />
<br />
6 .<br />
SIN ENTER<br />
These keystrokes yield the correct<br />
value of 0.5. Note that some<br />
calculators automatically place a<br />
left parenthesis after trigonometric<br />
functions. Check the user’s guide<br />
for your calculator for specific<br />
keystrokes on how to evaluate<br />
trigonometric functions.<br />
a. Because you have sin 13<br />
6 sin 2 <br />
6 sin 6 1 6 2 <br />
6 ,<br />
2 .<br />
b. Because 7<br />
you have<br />
2 4 <br />
2 ,<br />
c. For sin t 4 sint 4 because the sine function is odd.<br />
5 ,<br />
5<br />
Now try Exercise 37.<br />
Evaluating Trigonometric Functions with a Calculator<br />
When evaluating a trigonometric function with a calculator, you need to set the<br />
calculator to the desired mode of measurement (degree or radian).<br />
Most calculators do not have keys for the cosecant, secant, and cotangent<br />
functions. To evaluate these functions, you can use the x 1 key with their respective<br />
reciprocal functions sine, cosine, and tangent. For instance, to evaluate csc8, use<br />
the fact that<br />
<br />
csc<br />
8 1<br />
sin8<br />
and enter the following keystroke sequence in radian mode.<br />
SIN 8 x 1 ENTER Display 2.6131259<br />
Example 4<br />
13<br />
<br />
<br />
cos 7<br />
2<br />
cos 4 <br />
<br />
Using a Calculator<br />
Function Mode Calculator Keystrokes Display<br />
a. sin 2 Radian SIN 2 3 ENTER 0.8660254<br />
3<br />
b. cot 1.5 Radian TAN 1.5 x 1 ENTER 0.0709148<br />
Now try Exercise 55.<br />
<br />
<br />
2 cos 2 0.
Section 4.2 Trigonometric Functions: The Unit Circle 297<br />
4.2 EXERCISES<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
VOCABULARY: Fill in the blanks.<br />
1. Each real number t corresponds to a point x, y on the ________ ________.<br />
2. A function f is ________ if there exists a positive real number c such that f t c f t for all t in the domain of f.<br />
3. The smallest number c for which a function f is periodic is called the ________ of f.<br />
4. A function f is ________ if f t f t and ________ if f t f t.<br />
SKILLS AND APPLICATIONS<br />
In Exercises 5–8, determine the exact values of the six<br />
trigonometric functions of the real number t.<br />
5. y<br />
6.<br />
12 5<br />
,<br />
7. y<br />
8.<br />
t<br />
(<br />
4 3<br />
− , −<br />
5 5<br />
In Exercises 9–16, find the point x, y on the unit circle that<br />
corresponds to the real number t.<br />
<br />
9. t <br />
10. t <br />
2<br />
<br />
11. t <br />
12. t <br />
4<br />
3<br />
13. t 5<br />
14.<br />
6<br />
15. t 4<br />
16.<br />
3<br />
In Exercises 17–26, evaluate (if possible) the sine, cosine, and<br />
tangent of the real number.<br />
<br />
17. t <br />
18. t <br />
4<br />
3<br />
<br />
19. t <br />
20. t <br />
6<br />
4<br />
21. t 7<br />
22.<br />
4<br />
<br />
t 3<br />
4<br />
t 5<br />
3<br />
<br />
<br />
t 4<br />
3<br />
(<br />
x<br />
12 5<br />
, −<br />
13 13<br />
(<br />
(<br />
θ<br />
(<br />
θ<br />
13 13<br />
t<br />
x<br />
x<br />
(<br />
8 15<br />
− ,<br />
17 17<br />
t<br />
θ<br />
(<br />
(<br />
y<br />
y<br />
θ<br />
t<br />
x<br />
23. t 11<br />
24.<br />
6<br />
25. t 3<br />
26. t 2<br />
2<br />
In Exercises 27–34, evaluate (if possible) the six trigonometric<br />
functions of the real number.<br />
27. t 2<br />
28.<br />
3<br />
29. t 4<br />
30.<br />
3<br />
31. t 3<br />
32.<br />
4<br />
<br />
33. t <br />
34. t <br />
2<br />
In Exercises 35– 42, evaluate the trigonometric function<br />
using its period as an aid.<br />
35. sin 4<br />
36. cos 3<br />
37. cos 7<br />
38.<br />
3<br />
39. cos 17<br />
40.<br />
4<br />
41. sin 8<br />
42.<br />
3<br />
<br />
In Exercises 43–48, use the value of the trigonometric<br />
function to evaluate the indicated functions.<br />
43. sin t 1 2<br />
44. sint 3 8<br />
(a) sint<br />
(a) sin t<br />
(b) csct<br />
(b) csc t<br />
45. cost 1 5 46. cos t 3 4<br />
(a) cos t<br />
(a) cost<br />
(b) sect<br />
(b) sect<br />
47. sin t 4 5<br />
48. cos t 4 5<br />
(a)<br />
(a)<br />
(b) sint <br />
(b) cost <br />
sin t<br />
t 5<br />
3<br />
t 5<br />
6<br />
t 7<br />
4<br />
t 3<br />
2<br />
sin 9<br />
4<br />
sin 19<br />
6<br />
cos 9<br />
4<br />
<br />
cos t
298 Chapter 4 Trigonometry<br />
In Exercises 49–58, use a calculator to evaluate the trigonometric<br />
function. Round your answer to four decimal places.<br />
(Be sure the calculator is set in the correct angle mode.)<br />
51. cot<br />
52.<br />
4<br />
59. HARMONIC MOTION The displacement from<br />
equilibrium of an oscillating weight suspended by a<br />
spring is given by yt 1 4 cos 6t, where y is the<br />
displacement (in feet) and t is the time (in seconds). Find<br />
the displacements when (a) t 0, (b) t 1 and (c) t 1 4 ,<br />
2 .<br />
60. HARMONIC MOTION The displacement from<br />
equilibrium of an oscillating weight suspended by a<br />
spring and subject to the damping effect of friction is<br />
given by yt 1 4 et cos 6t, where y is the displacement<br />
(in feet) and t is the time (in seconds).<br />
(a) Complete the table.<br />
(b) Use the table feature of a graphing utility to approximate<br />
the time when the weight reaches equilibrium.<br />
(c) What appears to happen to the displacement as<br />
increases?<br />
EXPLORATION<br />
TRUE OR FALSE? In Exercises 61– 64, determine whether<br />
the statement is true or false. Justify your answer.<br />
61. Because sint sin t, it can be said that the sine of<br />
a negative angle is a negative number.<br />
62. tan a tana 6<br />
63. The real number 0 corresponds to the point 0, 1 on the<br />
unit circle.<br />
64.<br />
<br />
49. sin<br />
50. tan<br />
4<br />
3<br />
<br />
53. cos1.7<br />
54. cos2.5<br />
55. csc 0.8<br />
56. sec 1.8<br />
57. sec22.8<br />
58. cot0.9<br />
t 0<br />
1<br />
4<br />
cos 7<br />
2 cos <br />
y<br />
<br />
2<br />
csc 2<br />
3<br />
65. Let x 1 , y 1 and x 2 , y 2 be points on the unit circle<br />
corresponding to t t 1 and t t 1 , respectively.<br />
(a) Identify the symmetry of the points x 1 , y 1 and<br />
x 2 , y 2 .<br />
1<br />
2<br />
<br />
3<br />
4<br />
1<br />
t<br />
(b) Make a conjecture about any relationship between<br />
sin t 1 and sin t 1 .<br />
(c) Make a conjecture about any relationship between<br />
cos t 1 and<br />
cos t 1 .<br />
66. Use the unit circle to verify that the cosine and secant<br />
functions are even and that the sine, cosecant, tangent,<br />
and cotangent functions are odd.<br />
67. Verify that cos 2t 2 cos t by approximating cos 1.5<br />
and 2 cos 0.75.<br />
68. Verify that sint 1 t 2 sin t 1 sin t 2 by approximating<br />
sin 0.25, sin 0.75, and sin 1.<br />
69. THINK ABOUT IT Because ft sin t is an odd<br />
function and gt cos t is an even function, what can<br />
be said about the function ht ftgt?<br />
70. THINK ABOUT IT Because ft sin t and<br />
gt tan t are odd functions, what can be said about<br />
the function ht ftgt?<br />
71. GRAPHICAL ANALYSIS With your graphing utility in<br />
radian and parametric modes, enter the equations<br />
X1T cos T and Y1T sin T<br />
and use the following settings.<br />
Tmin 0, Tmax 6.3, Tstep 0.1<br />
Xmin 1.5, Xmax 1.5, Xscl 1<br />
Ymin 1, Ymax 1, Yscl 1<br />
(a) Graph the entered equations and describe the graph.<br />
(b) Use the trace feature to move the cursor around the<br />
graph. What do the t-values represent? What do the<br />
x- and y-values represent?<br />
(c) What are the least and greatest values of x and y?<br />
72. CAPSTONE A student you are tutoring has used a<br />
unit circle divided into 8 equal parts to complete the<br />
table for selected values of t. What is wrong?<br />
t 0<br />
x 1<br />
y 0<br />
sin t 1<br />
cos t 0<br />
<br />
4<br />
2<br />
2<br />
2<br />
2<br />
2<br />
2<br />
2<br />
2<br />
<br />
2<br />
3<br />
4<br />
0 2<br />
2<br />
1<br />
2<br />
2<br />
0 2<br />
2<br />
1<br />
2<br />
2<br />
<br />
1<br />
0<br />
1<br />
tan t Undef. 1 0 1 Undef.<br />
0
Section 4.3 Right Triangle Trigonometry 299<br />
4.3 RIGHT TRIANGLE TRIGONOMETRY<br />
Joseph Sohm/Visions of America/Corbis<br />
What you should learn<br />
• Evaluate trigonometric functions<br />
of acute angles.<br />
• Use fundamental trigonometric<br />
identities.<br />
• Use a calculator to evaluate<br />
trigonometric functions.<br />
• Use trigonometric functions to<br />
model and solve real-life problems.<br />
Why you should learn it<br />
Trigonometric functions are often used<br />
to analyze real-life situations. For<br />
instance, in Exercise 76 on page 309,<br />
you can use trigonometric functions<br />
to find the height of a helium-filled<br />
balloon.<br />
The Six Trigonometric Functions<br />
Our second look at the trigonometric functions is from a right triangle perspective.<br />
Consider a right triangle, with one acute angle labeled , as shown in Figure 4.26.<br />
Relative to the angle , the three sides of the triangle are the hypotenuse, the<br />
opposite side (the side opposite the angle ), and the adjacent side (the side adjacent to<br />
the angle ).<br />
<br />
FIGURE 4.26<br />
Hypotenuse<br />
Using the lengths of these three sides, you can form six ratios that define the six<br />
trigonometric functions of the acute angle .<br />
sine cosecant cosine secant tangent cotangent<br />
θ<br />
<br />
Side adjacent to θ<br />
In the following definitions, it is important to see that 0 < < 90 lies in the first<br />
quadrant) and that for such angles the value of each trigonometric function is positive.<br />
Right Triangle Definitions of Trigonometric Functions<br />
<br />
<br />
Let be an acute angle of a right triangle. The six trigonometric functions of the<br />
angle are defined as follows. (Note that the functions in the second row are the<br />
reciprocals of the corresponding functions in the first row.)<br />
sin<br />
csc<br />
opp<br />
hyp<br />
hyp<br />
opp<br />
cos<br />
adj<br />
hyp<br />
sec hyp<br />
adj<br />
The abbreviations opp, adj, and hyp represent the lengths of the three sides of a<br />
right triangle.<br />
opp the length of the side opposite<br />
adj the length of the side adjacent to<br />
hyp the length of the hypotenuse<br />
<br />
<br />
Side opposite θ<br />
<br />
tan opp<br />
adj<br />
cot adj<br />
opp
300 Chapter 4 Trigonometry<br />
Example 1<br />
Evaluating Trigonometric Functions<br />
θ<br />
FIGURE 4.27<br />
Hypotenuse<br />
3<br />
You can review the Pythagorean<br />
Theorem in Section 1.1.<br />
HISTORICAL NOTE<br />
Georg Joachim Rhaeticus<br />
(1514–1574) was the leading<br />
Teutonic mathematical<br />
astronomer of the 16th century.<br />
He was the first to define the<br />
trigonometric functions as ratios<br />
of the sides of a right triangle.<br />
4<br />
Use the triangle in Figure 4.27 to find the values of the six trigonometric functions of .<br />
Solution<br />
By the Pythagorean Theorem, hyp 2 opp 2 adj 2 , it follows that<br />
hyp 4 2 3 2<br />
So, the six trigonometric functions of<br />
sin<br />
25<br />
5.<br />
opp<br />
cos adj<br />
tan opp<br />
adj 4 3<br />
Now try Exercise 7.<br />
are<br />
In Example 1, you were given the lengths of two sides of the right triangle, but not<br />
the angle . Often, you will be asked to find the trigonometric functions of a given acute<br />
angle . To do <strong>this</strong>, construct a right triangle having as one of its angles.<br />
Example 2<br />
hyp 4 5<br />
hyp 3 5<br />
csc<br />
sec<br />
cot<br />
hyp<br />
hyp<br />
adj<br />
opp 5 4<br />
adj 5 3<br />
opp 3 4 .<br />
Evaluating Trigonometric Functions of 45<br />
Find the values of sin 45, cos 45, and tan 45.<br />
<br />
<br />
2<br />
45°<br />
1<br />
Solution<br />
Construct a right triangle having 45 as one of its acute angles, as shown in Figure 4.28.<br />
Choose the length of the adjacent side to be 1. From geometry, you know that the other<br />
acute angle is also 45. So, the triangle is isosceles and the length of the opposite side<br />
is also 1. Using the Pythagorean Theorem, you find the length of the hypotenuse to<br />
be2.<br />
45°<br />
FIGURE 4.28<br />
1<br />
sin 45 opp<br />
hyp <br />
cos 45 adj<br />
hyp <br />
1 2 2<br />
2<br />
1<br />
2 2<br />
2<br />
tan 45 opp<br />
adj 1 1 1<br />
Now try Exercise 23.
Section 4.3 Right Triangle Trigonometry 301<br />
Example 3<br />
Evaluating Trigonometric Functions of 30<br />
and 60<br />
Because the angles 30, 45, and<br />
60 6, 4, and 3 occur<br />
frequently in trigonometry, you<br />
should learn to construct the<br />
triangles shown in Figures 4.28<br />
and 4.29.<br />
Use the equilateral triangle shown in Figure 4.29 to find the values of<br />
cos 60, sin 30, and cos 30.<br />
30°<br />
2 3 2<br />
sin 60,<br />
1<br />
FIGURE 4.29<br />
60°<br />
1<br />
TECHNOLOGY<br />
You can use a calculator to<br />
convert the answers in Example 3<br />
to decimals. However, the<br />
radical form is the exact value<br />
and in most cases, the exact<br />
value is preferred.<br />
Solution<br />
Use the Pythagorean Theorem and the equilateral triangle in Figure 4.29 to verify the<br />
lengths of the sides shown in the figure. For you have adj 1, opp 3, and<br />
hyp 2. So,<br />
opp<br />
sin 60 <br />
hyp 3<br />
2<br />
30,<br />
and<br />
For adj 3, opp 1, and hyp 2. So,<br />
opp<br />
sin 30 <br />
hyp 1 2<br />
and<br />
Now try Exercise 27.<br />
60,<br />
cos 60 adj<br />
hyp 1 2 .<br />
cos 30 adj<br />
hyp 3<br />
2 .<br />
Sines, Cosines, and Tangents of Special Angles<br />
sin 30 sin<br />
cos 30 cos<br />
tan 30 tan<br />
6 3<br />
6 3<br />
6 1 2<br />
2<br />
3<br />
<br />
<br />
sin 45 sin<br />
4 2<br />
2<br />
<br />
sin 60 sin<br />
3 3<br />
2<br />
cos 45 cos<br />
cos 60 cos<br />
<br />
<br />
4 2<br />
2<br />
<br />
3 1 2<br />
<br />
<br />
tan 45 tan<br />
4 1<br />
<br />
tan 60 tan<br />
3 3<br />
In the box, note that sin 30 1 2 cos 60. This occurs because 30 and 60 are<br />
complementary angles. In general, it can be shown from the right triangle definitions<br />
that cofunctions of complementary angles are equal. That is, if is an acute angle, the<br />
following relationships are true.<br />
sin90 cos<br />
tan90 cot<br />
sec90 csc<br />
<br />
<br />
<br />
cos90 sin<br />
cot90 tan<br />
csc90 sec
302 Chapter 4 Trigonometry<br />
Trigonometric Identities<br />
In trigonometry, a great deal of time is spent studying relationships between trigonometric<br />
functions (identities).<br />
Fundamental Trigonometric Identities<br />
Reciprocal Identities<br />
sin<br />
csc<br />
Quotient Identities<br />
Pythagorean Identities<br />
sin 2<br />
<br />
<br />
1<br />
csc<br />
<br />
<br />
1<br />
sin<br />
tan sin<br />
cos<br />
<br />
<br />
cos 2 1<br />
cos 1<br />
sec<br />
sec<br />
cot<br />
<br />
<br />
1<br />
cos<br />
cos <br />
<br />
sin<br />
<br />
1 tan 2<br />
1 cot 2 csc 2<br />
tan<br />
cot<br />
sec 2 <br />
<br />
<br />
<br />
1<br />
cot<br />
<br />
<br />
1<br />
tan<br />
Note that sin 2 represents sin 2 , cos 2 represents cos 2 , and so on.<br />
<br />
Example 4<br />
Applying Trigonometric Identities<br />
θ<br />
FIGURE 4.30<br />
1<br />
0.8<br />
0.6<br />
<br />
Let be an acute angle such that sin Find the values of (a) cos and<br />
(b) tan using trigonometric identities.<br />
<br />
Solution<br />
a. To find the value of cos , use the Pythagorean identity<br />
sin 2 cos 2 1.<br />
So, you have<br />
0.6 2 cos 2 1<br />
Substitute 0.6 for sin .<br />
Subtract 0.6 2 from each side.<br />
Extract the positive square root.<br />
b. Now, knowing the sine and cosine of , you can find the tangent of to be<br />
tan<br />
cos<br />
sin <br />
<br />
cos<br />
0.6<br />
0.8<br />
cos 2 1 0.6 2 0.64<br />
0.75.<br />
0.64 0.8.<br />
<br />
Use the definitions of cos and tan , and the triangle shown in Figure 4.30, to check<br />
these results.<br />
Now try Exercise 33.<br />
0.6.
Section 4.3 Right Triangle Trigonometry 303<br />
Example 5<br />
Applying Trigonometric Identities<br />
<br />
Let be an acute angle such that tan Find the values of (a) cot and<br />
(b) sec using trigonometric identities.<br />
<br />
Solution<br />
<br />
<br />
1<br />
3.<br />
a. cot<br />
Reciprocal identity<br />
tan<br />
<br />
10<br />
θ<br />
1<br />
FIGURE 4.31<br />
3<br />
cot 1 3<br />
b. sec 2 1 tan 2 <br />
Pythagorean identity<br />
sec 2 1 3 2<br />
sec 2<br />
10<br />
sec 10<br />
<br />
Use the definitions of cot and sec , and the triangle shown in Figure 4.31, to check<br />
these results.<br />
Now try Exercise 35.<br />
You can also use the reciprocal<br />
identities for sine, cosine, and<br />
tangent to evaluate the cosecant,<br />
secant, and cotangent functions<br />
with a calculator. For instance,<br />
you could use the following<br />
keystroke sequence to evaluate<br />
sec 28.<br />
1 COS 28<br />
ENTER<br />
The calculator should display<br />
1.1325701.<br />
Evaluating Trigonometric Functions with a Calculator<br />
To use a calculator to evaluate trigonometric functions of angles measured in degrees,<br />
first set the calculator to degree mode and then proceed as demonstrated in Section 4.2.<br />
For instance, you can find values of cos 28 and sec 28 as follows.<br />
Function Mode Calculator Keystrokes Display<br />
a. cos 28 Degree COS 28 ENTER<br />
0.8829476<br />
b. sec 28 Degree <br />
28 1.1325701<br />
COS x 1 ENTER<br />
Throughout <strong>this</strong> text, angles are assumed to be measured in radians unless noted<br />
otherwise. For example, sin 1 means the sine of 1 radian and sin 1 means the sine of<br />
1 degree.<br />
Example 6 Using a Calculator<br />
Use a calculator to evaluate sec5 40 12.<br />
Solution<br />
Begin by converting to decimal degree form. [Recall that<br />
5 40 12 5 <br />
40<br />
60 <br />
12<br />
3600 5.67<br />
Then, use a calculator to evaluate sec 5.67.<br />
601 and<br />
Function Calculator Keystrokes Display<br />
sec5 40 12 sec 5.67<br />
Now try Exercise 51.<br />
<br />
COS<br />
<br />
1 1<br />
1 1<br />
5.67 x 1 ENTER 1.0049166<br />
36001.
304 Chapter 4 Trigonometry<br />
Observer<br />
Observer<br />
FIGURE 4.32<br />
Object<br />
Angle of<br />
elevation<br />
Horizontal<br />
Horizontal<br />
Angle of<br />
depression<br />
Object<br />
Applications Involving Right Triangles<br />
Many applications of trigonometry involve a process called solving right triangles. In<br />
<strong>this</strong> type of application, you are usually given one side of a right triangle and one of the<br />
acute angles and are asked to find one of the other sides, or you are given two sides and<br />
are asked to find one of the acute angles.<br />
In Example 7, the angle you are given is the angle of elevation, which represents<br />
the angle from the horizontal upward to an object. For objects that lie below the<br />
horizontal, it is common to use the term angle of depression, as shown in Figure 4.32.<br />
Example 7<br />
Using Trigonometry to Solve a Right Triangle<br />
A surveyor is standing 115 feet from the base of the Washington Monument, as shown<br />
in Figure 4.33. The surveyor measures the angle of elevation to the top of the monument<br />
as 78.3. How tall is the Washington Monument?<br />
y<br />
FIGURE 4.33<br />
x = 115 ft<br />
Angle of<br />
elevation<br />
78.3°<br />
Not drawn to scale<br />
Solution<br />
From Figure 4.33, you can see that<br />
tan 78.3 opp<br />
adj y x<br />
where x 115 and y is the height of the monument. So, the height of the Washington<br />
Monument is<br />
y x tan 78.3 1154.82882 555 feet.<br />
Now try Exercise 67.<br />
Example 8<br />
Using Trigonometry to Solve a Right Triangle<br />
A historic lighthouse is 200 yards from a bike path along the edge of a lake. A walkway<br />
to the lighthouse is 400 yards long. Find the acute angle between the bike path<br />
and the walkway, as illustrated in Figure 4.34.<br />
<br />
θ<br />
200 yd<br />
400 yd<br />
FIGURE 4.34<br />
Solution<br />
From Figure 4.34, you can see that the sine of the angle<br />
sin<br />
opp<br />
hyp 200<br />
400 1 2 .<br />
Now you should recognize that<br />
30.<br />
Now try Exercise 69.<br />
<br />
is
Section 4.3 Right Triangle Trigonometry 305<br />
By now you are able to recognize that is the acute angle that satisfies the<br />
equation sin Suppose, however, that you were given the equation sin<br />
and were asked to find the acute angle . Because<br />
1 2 .<br />
30<br />
0.6<br />
sin 30 1 2<br />
and<br />
0.5000<br />
sin 45 <br />
1 2<br />
0.7071<br />
<br />
you might guess that lies somewhere between 30 and 45. In a later section, you will<br />
study a method by which a more precise value of can be determined.<br />
<br />
Example 9<br />
Solving a Right Triangle<br />
Find the length c of the skateboard ramp shown in Figure 4.35.<br />
18.4°<br />
c<br />
4 ft<br />
Solution<br />
FIGURE 4.35<br />
From Figure 4.35, you can see that<br />
sin 18.4 opp<br />
hyp<br />
So, the length of the skateboard ramp is<br />
c <br />
4 c .<br />
4<br />
sin 18.4<br />
4<br />
0.3156<br />
12.7 feet.<br />
Now try Exercise 71.
306 Chapter 4 Trigonometry<br />
4.3<br />
VOCABULARY<br />
EXERCISES<br />
1. Match the trigonometric function with its right triangle definition.<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
(a) Sine (b) Cosine (c) Tangent (d) Cosecant (e) Secant (f) Cotangent<br />
hypotenuse adjacent hypotenuse adjacent opposite<br />
(i) (ii) (iii) (iv) (v) (vi)<br />
adjacent opposite opposite hypotenuse hypotenuse<br />
In Exercises 2–4, fill in the blanks.<br />
2. Relative to the angle , the three sides of a right triangle are the ________ side, the ________ side, and the ________.<br />
3. Cofunctions of ________ angles are equal.<br />
4. An angle that measures from the horizontal upward to an object is called the angle of ________, whereas an angle that<br />
measures from the horizontal downward to an object is called the angle of ________.<br />
SKILLS AND APPLICATIONS<br />
opposite<br />
adjacent<br />
In Exercises 5–8, find the exact values of the six trigonometric<br />
functions of the angle shown in the figure. (Use the<br />
Pythagorean Theorem to find the third side of the triangle.)<br />
5. 6.<br />
13<br />
5<br />
6<br />
θ<br />
θ<br />
8<br />
7. 41<br />
8.<br />
θ<br />
9<br />
4<br />
θ<br />
4<br />
In Exercises 9 –12, find the exact values of the six<br />
trigonometric functions of the angle for each of the two<br />
triangles. Explain why the function values are the same.<br />
9. 10. 1.25<br />
8<br />
θ<br />
15<br />
4<br />
θ<br />
7.5<br />
11. 3 12.<br />
1<br />
θ<br />
6<br />
2<br />
θ<br />
<br />
<br />
θ 1<br />
5<br />
θ<br />
4<br />
θ<br />
1<br />
2<br />
3<br />
θ<br />
6<br />
In Exercises 13–20, sketch a right triangle corresponding to<br />
the trigonometric function of the acute angle . Use the<br />
Pythagorean Theorem to determine the third side and then<br />
find the other five trigonometric functions of .<br />
13. tan<br />
14. cos<br />
15. sec<br />
16. tan<br />
19. cot<br />
20. csc<br />
In Exercises 21–30, construct an appropriate triangle to<br />
complete the table. 0 90, 0 /2<br />
21. sin<br />
22. cos<br />
23. sec<br />
24. tan<br />
25. cot<br />
26. csc<br />
27. csc<br />
28. sin<br />
Function (deg) (rad) Function Value<br />
29. cot 1<br />
30. tan<br />
3 4<br />
3 2<br />
1 5<br />
3<br />
17. sin<br />
18. sec<br />
<br />
30<br />
45<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
4<br />
<br />
3<br />
<br />
<br />
<br />
6<br />
<br />
4<br />
<br />
<br />
5 6<br />
4 5<br />
<br />
<br />
17 7<br />
9<br />
<br />
<br />
<br />
<br />
<br />
3<br />
3<br />
2<br />
<br />
<br />
3<br />
3
Section 4.3 Right Triangle Trigonometry 307<br />
In Exercises 31–36, use the given function value(s), and<br />
trigonometric identities (including the cofunction identities),<br />
to find the indicated trigonometric functions.<br />
31.<br />
32.<br />
33.<br />
34.<br />
35.<br />
36.<br />
(a)<br />
(c)<br />
(a)<br />
(c)<br />
cos 1 3<br />
(a) sin<br />
(c)<br />
(a)<br />
(c)<br />
(a)<br />
(c)<br />
(b)<br />
(b)<br />
(d)<br />
(b)<br />
(d)<br />
(b)<br />
(d)<br />
(b)<br />
(d)<br />
(b)<br />
(d)<br />
In Exercises 37– 46, use trigonometric identities to transform<br />
the left side of the equation into the right side<br />
0 < < /2.<br />
37.<br />
38.<br />
39.<br />
44.<br />
45.<br />
46.<br />
sin 60 3<br />
2 ,<br />
sec<br />
<br />
tan<br />
cos<br />
sin<br />
cos<br />
sin 30<br />
tan 60<br />
sin 30 1 2 ,<br />
csc 30<br />
cos 30<br />
sec<br />
<br />
<br />
<br />
<br />
5<br />
<br />
cos<br />
cot90 <br />
cot 5<br />
(a) tan <br />
(c) cot90 <br />
cos 7<br />
4<br />
sec <br />
cot <br />
cot 1<br />
sec 1<br />
tan cos sin <br />
tan<br />
cos<br />
sin<br />
<br />
<br />
cos 60 1 2<br />
csc<br />
tan<br />
sin 2 cos 2 2 sin 2 1<br />
tan cot <br />
csc 2 <br />
tan <br />
sec <br />
cos 30<br />
(d) cot 60<br />
tan 30 3<br />
3<br />
cot 60<br />
cot 30<br />
In Exercises 47–56, use a calculator to evaluate each function.<br />
Round your answers to four decimal places. (Be sure the<br />
calculator is in the correct angle mode.)<br />
cot<br />
sin<br />
40. cot sin cos <br />
41. 1 sin 1 sin cos 2 <br />
42. 1 cos 1 cos sin 2 <br />
43. sec sec 1<br />
47. (a) sin 10<br />
(b) cos 80<br />
<br />
tan<br />
csc90 <br />
<br />
<br />
csc <br />
cos <br />
sin <br />
sin90 <br />
48. (a) tan 23.5 (b) cot 66.5<br />
49. (a) sin 16.35 (b) csc 16.35<br />
50. (a) cot 79.56 (b) sec 79.56<br />
51. (a) cos 4 50 15 (b) sec 4 50 15<br />
52. (a) sec 42 12 (b) csc 48 7<br />
53. (a) cot 11 15 (b) tan 11 15<br />
54. (a) sec 56 8 10 (b) cos 56 8 10<br />
55. (a) csc 32 40 3 (b) tan 44 28 16<br />
56. (a) sec 9 (b) cot 9 5 20 32<br />
5 30 32<br />
In Exercises 57–62, find the values of in degrees<br />
0 < < 90 and radians 0 < < /2 without the aid<br />
of a calculator.<br />
<br />
57. (a) sin<br />
(b) csc<br />
58. (a) cos<br />
(b) tan<br />
2<br />
59. (a) sec<br />
(b) cot<br />
60. (a) tan<br />
(b) cos<br />
61. (a) csc<br />
(b) sin<br />
3<br />
62. (a) cot<br />
(b) sec<br />
3<br />
In Exercises 63–66, solve for x, y, or r as indicated.<br />
63. Solve for y.<br />
64. Solve for x.<br />
18 y<br />
60°<br />
65. Solve for x.<br />
66. Solve for r.<br />
60°<br />
x<br />
1 2<br />
2<br />
2<br />
3<br />
23<br />
3<br />
32<br />
2<br />
1<br />
1<br />
1 2<br />
2<br />
2<br />
30°<br />
45°<br />
67. EMPIRE STATE BUILDING You are standing 45 meters<br />
from the base of the Empire State Building. You<br />
estimate that the angle of elevation to the top of the 86th<br />
floor (the observatory) is 82. If the total height of the<br />
building is another 123 meters above the 86th floor,<br />
what is the approximate height of the building? One of<br />
your friends is on the 86th floor. What is the distance<br />
between you and your friend?<br />
<br />
r<br />
2<br />
x<br />
<br />
20<br />
30
308 Chapter 4 Trigonometry<br />
68. HEIGHT A six-foot person walks from the base of a<br />
broadcasting tower directly toward the tip of the<br />
shadow cast by the tower. When the person is 132 feet<br />
from the tower and 3 feet from the tip of the shadow, the<br />
person’s shadow starts to appear beyond the tower’s<br />
shadow.<br />
(a) Draw a right triangle that gives a visual<br />
representation of the problem. Show the known<br />
quantities of the triangle and use a variable to<br />
indicate the height of the tower.<br />
(b) Use a trigonometric function to write an equation<br />
involving the unknown quantity.<br />
(c) What is the height of the tower?<br />
69. ANGLE OF ELEVATION You are skiing down a<br />
mountain with a vertical height of 1500 feet. The<br />
distance from the top of the mountain to the base is<br />
3000 feet. What is the angle of elevation from the base<br />
to the top of the mountain?<br />
70. WIDTH OF A RIVER A biologist wants to know the<br />
width w of a river so that instruments for studying the<br />
pollutants in the water can be set properly. From point<br />
A, the biologist walks downstream 100 feet and sights to<br />
point C (see figure). From <strong>this</strong> sighting, it is determined<br />
that How wide is the river?<br />
54.<br />
w<br />
C<br />
θ = 54°<br />
A 100 ft<br />
71. LENGTH A guy wire runs from the ground to a cell<br />
tower. The wire is attached to the cell tower 150 feet<br />
above the ground. The angle formed between the wire<br />
and the ground is 43 (see figure).<br />
150 ft<br />
72. HEIGHT OF A MOUNTAIN In traveling across flat<br />
land, you notice a mountain directly in front of you. Its<br />
angle of elevation (to the peak) is 3.5. After you drive<br />
13 miles closer to the mountain, the angle of elevation<br />
is 9. Approximate the height of the mountain.<br />
73. MACHINE SHOP CALCULATIONS A steel plate has<br />
the form of one-fourth of a circle with a radius of<br />
60 centimeters. Two two-centimeter holes are to be<br />
drilled in the plate positioned as shown in the figure.<br />
Find the coordinates of the center of each hole.<br />
60<br />
56<br />
y<br />
(x 2<br />
, y 2<br />
)<br />
30°<br />
30°<br />
30°<br />
3.5° 9°<br />
13 mi<br />
(x 1<br />
, y 1<br />
)<br />
FIGURE FOR 73 FIGURE FOR 74<br />
74. MACHINE SHOP CALCULATIONS A tapered shaft<br />
has a diameter of 5 centimeters at the small end and is<br />
15 centimeters long (see figure). The taper is 3. Find<br />
the diameter d of the large end of the shaft.<br />
75. GEOMETRY Use a compass to sketch a quarter of a<br />
circle of radius 10 centimeters. Using a protractor,<br />
construct an angle of 20 in standard position (see<br />
figure). Drop a perpendicular line from the point of<br />
intersection of the terminal side of the angle and the<br />
arc of the circle. By actual measurement, calculate<br />
the coordinates x, y of the point of intersection<br />
and use these measurements to approximate the six<br />
trigonometric functions of a 20 angle.<br />
10<br />
y<br />
56 60<br />
x<br />
3°<br />
Not drawn to scale<br />
d<br />
5 cm<br />
15 cm<br />
θ = 43°<br />
(x, y)<br />
(a) How long is the guy wire?<br />
(b) How far from the base of the tower is the guy wire<br />
anchored to the ground?<br />
10 cm<br />
20°<br />
10<br />
x
Section 4.3 Right Triangle Trigonometry 309<br />
76. HEIGHT A 20-meter line is used to tether a<br />
helium-filled balloon. Because of a breeze, the line<br />
makes an angle of approximately 85 with the ground.<br />
(a) Draw a right triangle that gives a visual representation<br />
of the problem. Show the known quantities of<br />
the triangle and use a variable to indicate the height<br />
of the balloon.<br />
(b) Use a trigonometric function to write an equation<br />
involving the unknown quantity.<br />
(c) What is the height of the balloon?<br />
(d) The breeze becomes stronger and the angle the<br />
balloon makes with the ground decreases. How<br />
does <strong>this</strong> affect the triangle you drew in part (a)?<br />
(e) Complete the table, which shows the heights<br />
(in meters) of the balloon for decreasing angle<br />
measures .<br />
(f) As the angle the balloon makes with the ground<br />
approaches 0, how does <strong>this</strong> affect the height of the<br />
balloon? Draw a right triangle to explain your<br />
reasoning.<br />
EXPLORATION<br />
Angle,<br />
Height<br />
Angle,<br />
Height<br />
<br />
<br />
80 70 60 50<br />
40 30 20 10<br />
84. THINK ABOUT IT<br />
(a) Complete the table.<br />
<br />
sin<br />
cos<br />
<br />
<br />
0 18 36 54 72 90<br />
(b) Discuss the behavior of the sine function for in the<br />
range from 0 to 90.<br />
(c) Discuss the behavior of the cosine function for<br />
the range from 0 to 90.<br />
(d) Use the definitions of the sine and cosine functions<br />
to explain the results of parts (b) and (c).<br />
85. WRITING In right triangle trigonometry, explain why<br />
sin 30 1 2 regardless of the size of the triangle.<br />
86. GEOMETRY Use the equilateral triangle shown in<br />
Figure 4.29 and similar triangles to verify the points in<br />
Figure 4.23 (in Section 4.2) that do not lie on the axes.<br />
87. THINK ABOUT IT You are given only the value tan .<br />
Is it possible to find the value of sec without finding<br />
the measure of ? Explain.<br />
88. CAPSTONE The Johnstown Inclined Plane in<br />
Pennsylvania is one of the longest and steepest hoists<br />
in the world. The railway cars travel a distance of<br />
896.5 feet at an angle of approximately 35.4, rising to<br />
a height of 1693.5 feet above sea level.<br />
<br />
<br />
in<br />
TRUE OR FALSE? In Exercises 77–82, determine whether<br />
the statement is true or false. Justify your answer.<br />
77. sin 60 csc 60 1 78. sec 30 csc 60<br />
79. sin 45 cos 45 1 80. cot 2 10 csc 2 10 1<br />
sin 60<br />
81. sin 2 82. tan5 2 tan 2 5<br />
sin 30<br />
35.4°<br />
896.5 ft<br />
1693.5 feet<br />
above sea level<br />
Not drawn to scale<br />
83. THINK ABOUT IT<br />
(a) Complete the table.<br />
<br />
(b) Is or sin greater for in the interval 0, 0.5?<br />
<br />
<br />
sin<br />
<br />
<br />
0.1 0.2 0.3 0.4 0.5<br />
(c) As approaches 0, how do and sin compare?<br />
Explain.<br />
<br />
<br />
<br />
(a) Find the vertical rise of the inclined plane.<br />
(b) Find the elevation of the lower end of the inclined<br />
plane.<br />
(c) The cars move up the mountain at a rate of<br />
300 feet per minute. Find the rate at which they rise<br />
vertically.
310 Chapter 4 Trigonometry<br />
4.4 TRIGONOMETRIC FUNCTIONS OF ANY ANGLE<br />
What you should learn<br />
• Evaluate trigonometric functions<br />
of any angle.<br />
• Find reference angles.<br />
• Evaluate trigonometric functions of<br />
real numbers.<br />
Why you should learn it<br />
You can use trigonometric functions<br />
to model and solve real-life problems.<br />
For instance, in Exercise 99 on page<br />
318, you can use trigonometric<br />
functions to model the monthly<br />
normal temperatures in New York City<br />
and Fairbanks, Alaska.<br />
Introduction<br />
In Section 4.3, the definitions of trigonometric functions were restricted to acute angles.<br />
In <strong>this</strong> section, the definitions are extended to cover any angle. If is an acute angle,<br />
these definitions coincide with those given in the preceding section.<br />
Definitions of Trigonometric Functions of Any Angle<br />
Let be an angle in standard position with x, y a point on the terminal side of<br />
and r x 2 y 2 0.<br />
<br />
y<br />
sin<br />
cos x r<br />
( x, y)<br />
tan y x , x 0<br />
sec<br />
y r<br />
cot x y , y 0<br />
r x , x 0<br />
csc r y , y 0<br />
r<br />
<br />
θ<br />
x<br />
<br />
Because r x 2 y 2 cannot be zero, it follows that the sine and cosine<br />
functions are defined for any real value of . However, if x 0, the tangent and secant<br />
of are undefined. For example, the tangent of 90 is undefined. Similarly, if y 0, the<br />
cotangent and cosecant of are undefined.<br />
<br />
<br />
Example 1<br />
Evaluating Trigonometric Functions<br />
James Urbach/SuperStock<br />
Let 3, 4 be a point on the terminal side of . Find the sine, cosine, and tangent of .<br />
Solution<br />
Referring to Figure 4.36, you can see that x 3, y 4, and<br />
r x 2 y 2 3 2 4 2 25 5.<br />
So, you have the following.<br />
sin<br />
y r 4 5<br />
cos<br />
x r 3 5<br />
tan<br />
y x 4 3<br />
y<br />
( −3, 4)<br />
r<br />
4<br />
3<br />
2<br />
The formula r x 2 y 2 is<br />
a result of the Distance Formula.<br />
You can review the Distance<br />
Formula in Section 1.1.<br />
Now try Exercise 9.<br />
1<br />
θ<br />
−3 −2 −1 1<br />
FIGURE 4.36<br />
x
Section 4.4 Trigonometric Functions of Any Angle 311<br />
π<br />
2 < θ < π<br />
x < 0<br />
y > 0<br />
y<br />
0 < θ <<br />
π<br />
2<br />
x > 0<br />
y > 0<br />
The signs of the trigonometric functions in the four quadrants can be determined<br />
from the definitions of the functions. For instance, because cos it follows that<br />
cos is positive wherever x > 0, which is in Quadrants I and IV. (Remember, r is<br />
always positive.) In a similar manner, you can verify the results shown in Figure 4.37.<br />
<br />
xr,<br />
x<br />
Example 2<br />
Evaluating Trigonometric Functions<br />
x < 0<br />
y < 0<br />
π<br />
< θ <<br />
3π<br />
2<br />
y<br />
x > 0<br />
y < 0<br />
3π<br />
2 < θ < 2π<br />
Given tan and cos > 0, find sin and<br />
Solution<br />
5 4<br />
<br />
<br />
<br />
sec .<br />
Note that lies in Quadrant IV because that is the only quadrant in which the tangent<br />
is negative and the cosine is positive. Moreover, using<br />
Quadrant II<br />
sin θ: +<br />
cos θθ :<br />
tan : −<br />
−<br />
Quadrant III<br />
sin θ:<br />
−<br />
cos θθ : −<br />
tan : +<br />
FIGURE 4.37<br />
Quadrant I<br />
sin θ: +<br />
cos θθ : +<br />
tan : +<br />
Quadrant IV<br />
sin θ:<br />
−<br />
cos θθ : +<br />
tan : −<br />
x<br />
tan y x<br />
5 4<br />
and the fact that y is negative in Quadrant IV, you can let y 5 and x 4. So,<br />
r 16 25 41 and you have<br />
sin y r 5<br />
41<br />
0.7809<br />
sec r x 41<br />
4<br />
1.6008.<br />
Now try Exercise 23.<br />
Example 3<br />
Trigonometric Functions of Quadrant Angles<br />
(−1, 0)<br />
FIGURE 4.38<br />
π<br />
2<br />
3π<br />
2<br />
y<br />
(0, 1)<br />
π 0<br />
(0, −1)<br />
(1, 0)<br />
x<br />
Evaluate the cosine and tangent functions at the four quadrant angles 0, and<br />
2 , ,<br />
2 .<br />
Solution<br />
To begin, choose a point on the terminal side of each angle, as shown in Figure 4.38.<br />
For each of the four points, r 1, and you have the following.<br />
cos 0 x tan 0 y x, y 1, 0<br />
x 0 r 1 1 1 1 0<br />
cos<br />
tan<br />
2 y x 1 2 x r 0 1 0 0 ⇒ undefined<br />
<br />
cos x tan y x, y 1, 0<br />
x 0<br />
r 1<br />
1 0<br />
3<br />
cos tan 3<br />
x, y 0, 1<br />
2 y x 1<br />
2 x r 0 1 0 0 ⇒ undefined<br />
1 1 x, y 0, 1<br />
Now try Exercise 37.<br />
<br />
<br />
3
312 Chapter 4 Trigonometry<br />
Reference Angles<br />
The values of the trigonometric functions of angles greater than 90 (or less than 0) can<br />
be determined from their values at corresponding acute angles called reference angles.<br />
Definition of Reference Angle<br />
<br />
Let be an angle in standard position. Its reference angle is the acute angle<br />
formed by the terminal side of and the horizontal axis.<br />
<br />
<br />
Figure 4.39 shows the reference angles for<br />
<br />
in Quadrants II, III, and IV.<br />
Quadrant II<br />
θ<br />
Reference<br />
angle: ′ θ<br />
θ<br />
θ<br />
Reference<br />
angle: ′ θ<br />
Reference<br />
angle: θ ′<br />
θ′ = π − θ (radians)<br />
θ ′ = 180° − θ (degrees)<br />
FIGURE 4.39<br />
Quadrant III<br />
θ ′ = θ − (radians)<br />
′ = θ − 180° π<br />
θ<br />
(degrees)<br />
Quadrant<br />
IV<br />
θ′ = 2π<br />
− θ (radians)<br />
θ′ = 360° − θ (degrees)<br />
y<br />
Example 4<br />
Finding Reference Angles<br />
θ = 300°<br />
x<br />
θ′ = 60°<br />
Find the reference angle .<br />
300<br />
2.3<br />
a. b. c.<br />
135<br />
FIGURE 4.40<br />
θ′ = π − 2.3<br />
FIGURE 4.41<br />
θ′ = 45°<br />
225°<br />
FIGURE 4.42<br />
y<br />
y<br />
θ = 2.3<br />
x<br />
225° and −135°<br />
are coterminal.<br />
x<br />
θ = −135°<br />
Solution<br />
a. Because 300 lies in Quadrant IV, the angle it makes with the x-axis is<br />
360 300<br />
60.<br />
Degrees<br />
Figure 4.40 shows the angle<br />
and its reference angle<br />
b. Because 2.3 lies between 2 1.5708 and it follows that it is in<br />
Quadrant II and its reference angle is<br />
2.3<br />
0.8416.<br />
Radians<br />
Figure 4.41 shows the angle<br />
and its reference angle<br />
c. First, determine that 135 is coterminal with 225, which lies in Quadrant III. So,<br />
the reference angle is<br />
225 180<br />
45.<br />
Degrees<br />
Figure 4.42 shows the angle<br />
2.3<br />
Now try Exercise 45.<br />
300<br />
135<br />
3.1416,<br />
and its reference angle<br />
60.<br />
2.3.<br />
45.
Section 4.4 Trigonometric Functions of Any Angle 313<br />
(x, y)<br />
y<br />
Trigonometric Functions of Real Numbers<br />
To see how a reference angle is used to evaluate a trigonometric function, consider the<br />
point x, y on the terminal side of , as shown in Figure 4.43. By definition, you know<br />
that<br />
opp<br />
r = hyp<br />
adj<br />
θ′<br />
opp y, adj x<br />
FIGURE 4.43<br />
θ<br />
x<br />
and<br />
For the right triangle with acute angle and sides of lengths and you have<br />
sin<br />
hyp y <br />
r<br />
and<br />
sin<br />
tan<br />
So, it follows that sin and sin are equal, except possibly in sign. The same is true<br />
for tan and tan and for the other four trigonometric functions. In all cases, the sign<br />
of the function value can be determined by the quadrant in which lies.<br />
<br />
y r<br />
opp<br />
opp<br />
adj y <br />
<br />
x .<br />
<br />
tan<br />
y x .<br />
<br />
<br />
x <br />
<br />
y ,<br />
Evaluating Trigonometric Functions of Any Angle<br />
To find the value of a trigonometric function of any angle :<br />
1. Determine the function value for the associated reference angle .<br />
2. Depending on the quadrant in which lies, affix the appropriate sign to the<br />
function value.<br />
<br />
Learning the table of values<br />
at the right is worth the effort<br />
because doing so will increase<br />
both your efficiency and your<br />
confidence. Here is a pattern<br />
for the sine function that may<br />
help you remember the values.<br />
<br />
sin<br />
<br />
0 30 45 60 90<br />
0<br />
2<br />
1<br />
2<br />
2<br />
2<br />
3<br />
2<br />
4<br />
2<br />
Reverse the order to get cosine<br />
values of the same angles.<br />
By using reference angles and the special angles discussed in the preceding<br />
section, you can greatly extend the scope of exact trigonometric values. For instance,<br />
knowing the function values of 30 means that you know the function values of all<br />
angles for which 30 is a reference angle. For convenience, the table below shows the<br />
exact values of the trigonometric functions of special angles and quadrant angles.<br />
Trigonometric Values of Common Angles<br />
<br />
<br />
sin<br />
cos<br />
tan<br />
(degrees)<br />
(radians)<br />
<br />
<br />
<br />
0 30 45 60 90 180 270<br />
0<br />
0<br />
1<br />
0<br />
<br />
6<br />
1<br />
2<br />
3<br />
2<br />
3<br />
3<br />
<br />
4<br />
2<br />
2<br />
2<br />
2<br />
<br />
3<br />
3<br />
2<br />
1<br />
2<br />
<br />
2<br />
<br />
3<br />
2<br />
1 0 1<br />
0 1 0<br />
1 3 Undef. 0 Undef.
314 Chapter 4 Trigonometry<br />
Example 5<br />
Using Reference Angles<br />
Evaluate each trigonometric function.<br />
a. cos 4 b. tan210 c.<br />
3<br />
Solution<br />
a. Because lies in Quadrant III, the reference angle is<br />
4<br />
43<br />
as shown in Figure 6.41. Moreover, the cosine is negative in Quadrant III, so<br />
1 2 .<br />
b. Because 210 360 150, it follows that 210 is coterminal with the<br />
second-quadrant angle 150. So, the reference angle is 180 150 30, as<br />
shown in Figure 4.45. Finally, because the tangent is negative in Quadrant II, you<br />
have<br />
c. Because 114 2 34, it follows that 114 is coterminal with the<br />
second-quadrant angle 34. So, the reference angle is as<br />
shown in Figure 4.46. Because the cosecant is positive in Quadrant II, you have<br />
csc 11<br />
4 csc<br />
<br />
1<br />
sin4<br />
2.<br />
<br />
3 <br />
3<br />
cos 4 cos<br />
3<br />
<br />
tan210 tan 30<br />
3<br />
3<br />
3 .<br />
<br />
4<br />
csc 11<br />
4<br />
<br />
34 4,<br />
y<br />
y<br />
y<br />
θ′ =<br />
π<br />
3<br />
θ =<br />
4π<br />
3<br />
x<br />
θ′ = 30°<br />
θ = −210°<br />
x<br />
θ′ =<br />
π<br />
4<br />
θ =<br />
11π<br />
4<br />
x<br />
FIGURE 4.44 FIGURE 4.45 FIGURE 4.46<br />
Now try Exercise 59.
Section 4.4 Trigonometric Functions of Any Angle 315<br />
Example 6<br />
Using Trigonometric Identities<br />
<br />
Let be an angle in Quadrant II such that sin Find (a) cos and (b) tan by<br />
using trigonometric identities.<br />
Solution<br />
a. Using the Pythagorean identity sin 2 cos 2 1, you obtain<br />
1 3 2 cos 2<br />
Because cos<br />
cos 8<br />
9<br />
Substitute 3 for sin .<br />
cos 2 1 1 9 8 9 .<br />
<br />
< 0 in Quadrant II, you can use the negative root to obtain<br />
22<br />
3 .<br />
b. Using the trigonometric identity tan , you obtain<br />
cos<br />
tan 13<br />
223<br />
1<br />
22<br />
2<br />
4 .<br />
1<br />
Now try Exercise 69.<br />
sin <br />
<br />
1 3 .<br />
Substitute for sin<br />
You can use a calculator to evaluate trigonometric functions, as shown in the next<br />
example.<br />
1<br />
<br />
and<br />
<br />
cos .<br />
<br />
Example 7<br />
Using a Calculator<br />
Use a calculator to evaluate each trigonometric function.<br />
a. cot 410 b. sin7 c. sec<br />
9<br />
Solution<br />
Function Mode Calculator Keystrokes Display<br />
a. cot 410 Degree TAN 410 x 1 ENTER 0.8390996<br />
b. sin7 Radian SIN 7 ENTER<br />
0.6569866<br />
<br />
c. sec Radian COS 9 <br />
1.0641778<br />
9<br />
x 1 ENTER<br />
Now try Exercise 79.
316 Chapter 4 Trigonometry<br />
4.4<br />
EXERCISES<br />
VOCABULARY: Fill in the blanks.<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
<br />
In Exercises 1–6, let be an angle in standard position, with x, y a point on the terminal side of and r x 2 1 y 2 0.<br />
________<br />
1. sin<br />
2.<br />
________<br />
3. tan<br />
4. sec<br />
x<br />
5. 6.<br />
r ________<br />
7. Because r x 2 y 2 cannot be ________, the sine and cosine functions are ________ for any real value of .<br />
8. The acute positive angle that is formed by the terminal side of the angle and the horizontal axis is called<br />
the ________ angle of and is denoted by .<br />
SKILLS AND APPLICATIONS<br />
<br />
r<br />
y ________<br />
________<br />
x<br />
y ________<br />
<br />
<br />
In Exercises 9–12, determine the exact values of the six<br />
trigonometric functions of the angle .<br />
9. (a) (b)<br />
(4, 3)<br />
10. (a) (b)<br />
θ<br />
11. (a) (b)<br />
θ<br />
y<br />
y<br />
(−12, −5)<br />
y<br />
( − 3, −1)<br />
y<br />
12. (a) (b)<br />
θ<br />
θ<br />
(3, 1)<br />
In Exercises 13–18, the point is on the terminal side of an<br />
angle in standard position. Determine the exact values of the<br />
six trigonometric functions of the angle.<br />
13. 5, 12<br />
14. 8, 15<br />
15. 5, 2<br />
16. 4, 10<br />
17. 5.4, 7.2<br />
18. 3 1 2, 7 3 4<br />
x<br />
x<br />
x<br />
x<br />
(−8, 15)<br />
θ<br />
θ<br />
(−4, 4)<br />
y<br />
y<br />
y<br />
y<br />
θ<br />
(1, −1)<br />
(4, −1)<br />
θ<br />
x<br />
x<br />
x<br />
x<br />
In Exercises 19–22, state the quadrant in which<br />
19. sin > 0 and cos<br />
20. sin < 0 and<br />
21. sin > 0 and cos<br />
22. sec > 0 and cot<br />
lies.<br />
In Exercises 23–32, find the values of the six trigonometric<br />
functions of with the given constraint.<br />
23.<br />
24.<br />
Function Value<br />
Constraint<br />
25. sin<br />
lies in Quadrant II.<br />
26. cos<br />
lies in Quadrant III.<br />
27.<br />
28.<br />
29.<br />
30.<br />
tan<br />
cos<br />
cot<br />
csc<br />
sec<br />
sin<br />
<br />
15<br />
8<br />
3 5<br />
4 5<br />
3<br />
4<br />
2<br />
0<br />
<br />
31. cot is undefined.<br />
<br />
32. tan is undefined.<br />
In Exercises 33–36, the terminal side of lies on the given<br />
line in the specified quadrant. Find the values of the six<br />
trigonometric functions of by finding a point on the line.<br />
Line<br />
<br />
17<br />
8<br />
cos < 0<br />
Quadrant<br />
33. y x<br />
II<br />
34. y 1 3 x<br />
III<br />
35. 2x y 0<br />
III<br />
36. 4x 3y 0<br />
IV<br />
<br />
<br />
<br />
> 0<br />
< 0<br />
< 0<br />
<br />
sin<br />
tan<br />
<br />
<br />
cos<br />
cot<br />
sin<br />
sec<br />
2 32<br />
2<br />
<br />
<br />
<br />
<br />
<br />
<br />
> 0<br />
< 0<br />
< 0<br />
< 0<br />
1<br />
<br />
> 0
Section 4.4 Trigonometric Functions of Any Angle 317<br />
In Exercises 37–44, evaluate the trigonometric function of<br />
the quadrant angle.<br />
37. sin <br />
38.<br />
In Exercises 45–52, find the reference angle , and sketch<br />
and in standard position.<br />
<br />
45. 46.<br />
47. 48.<br />
49. 50.<br />
3<br />
51. 52.<br />
In Exercises 53–68, evaluate the sine, cosine, and tangent of<br />
the angle without using a calculator.<br />
2<br />
59. 60.<br />
3<br />
5<br />
61. 62.<br />
4<br />
9<br />
<br />
<br />
160<br />
125<br />
2<br />
4.8<br />
65. 66.<br />
4<br />
67. 3<br />
68.<br />
2<br />
In Exercises 69–74, find the indicated trigonometric value in<br />
the specified quadrant.<br />
Function Quadrant Trigonometric Value<br />
3 5<br />
3<br />
69. sin<br />
IV<br />
70. cot<br />
II<br />
3 2<br />
2<br />
71. tan<br />
III<br />
72. csc<br />
IV<br />
5 8<br />
73. cos<br />
I<br />
9 4<br />
74. sec<br />
III<br />
csc 3<br />
2<br />
39. sec 3<br />
40. sec <br />
2<br />
41. sin<br />
42. cot <br />
2<br />
43. csc <br />
44. cot<br />
2<br />
53. 225<br />
54. 300<br />
55. 750<br />
56. 405<br />
57. 150<br />
58. 840<br />
3<br />
63. <br />
64. <br />
6<br />
2<br />
4<br />
7<br />
6<br />
10<br />
3<br />
<br />
<br />
309<br />
215<br />
7<br />
6<br />
11.6<br />
23<br />
4<br />
cos<br />
sin<br />
sec<br />
cot<br />
sec<br />
tan<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
In Exercises 75–90, use a calculator to evaluate the<br />
trigonometric function. Round your answer to four decimal<br />
places. (Be sure the calculator is set in the correct angle mode.)<br />
75. sin 10<br />
76. sec 225<br />
77. cos110<br />
78. csc330<br />
79. tan 304<br />
80. cot 178<br />
81. sec 72<br />
82. tan188<br />
83. tan 4.5<br />
84. cot 1.35<br />
85. tan<br />
86. tan <br />
9<br />
87. sin0.65<br />
88. sec 0.29<br />
89. cot 11<br />
8 <br />
90.<br />
In Exercises 91–96, find two solutions of the equation. Give<br />
your answers in degrees 0 < 360 and in radians<br />
0 < 2. Do not use a calculator.<br />
<br />
<br />
1 2<br />
91. (a) sin<br />
(b) sin<br />
2<br />
92. (a) cos<br />
(b) cos<br />
2<br />
23<br />
93. (a) csc<br />
(b) cot<br />
3<br />
2<br />
94. (a) sec<br />
(b) sec<br />
1<br />
95. (a) tan<br />
(b) cot<br />
3<br />
96. (a) sin<br />
(b) sin<br />
2<br />
97. DISTANCE An airplane, flying at an altitude of 6 miles,<br />
is on a flight path that passes directly over an observer<br />
(see figure). If is the angle of elevation from the<br />
observer to the plane, find the distance d from the<br />
observer to the plane when (a) (b)<br />
and (c)<br />
120.<br />
θ<br />
<br />
d<br />
1 2<br />
2<br />
1<br />
2<br />
3<br />
3<br />
30,<br />
90,<br />
6 mi<br />
Not drawn to scale<br />
98. HARMONIC MOTION The displacement from<br />
equilibrium of an oscillating weight suspended by a<br />
spring is given by yt 2 cos 6t, where y is the<br />
displacement (in centimeters) and t is the time (in<br />
seconds). Find the displacement when (a) t 0,<br />
(b) t 1 and (c) t 1 4 , 2 .<br />
<br />
<br />
9<br />
csc 15<br />
14 <br />
2<br />
2
318 Chapter 4 Trigonometry<br />
99. DATA ANALYSIS: METEOROLOGY The table<br />
shows the monthly normal temperatures (in degrees<br />
Fahrenheit) for selected months in New York City N<br />
and Fairbanks, Alaska F. (Source: National<br />
Climatic Data Center)<br />
(a) Use the regression feature of a graphing utility to<br />
find a model of the form y a sinbt c d<br />
for each city. Let t represent the month, with t 1<br />
corresponding to January.<br />
(b) Use the models from part (a) to find the monthly<br />
normal temperatures for the two cities in February,<br />
March, May, June, August, September, and<br />
November.<br />
(c) Compare the models for the two cities.<br />
100. SALES A company that produces snowboards, which are<br />
seasonal products, forecasts monthly sales over the next<br />
2 years to be S 23.1 0.442t 4.3 cost6,<br />
where S is measured in thousands of units and t is<br />
the time in months, with t 1 representing January<br />
2010. Predict sales for each of the following months.<br />
(a) February 2010 (b) February 2011<br />
(c) June 2010 (d) June 2011<br />
101. HARMONIC MOTION The displacement from<br />
equilibrium of an oscillating weight suspended by a<br />
spring and subject to the damping effect of friction<br />
is given by yt 2e t cos 6t, where y is the<br />
displacement (in centimeters) and t is the time (in<br />
seconds). Find the displacement when (a) t 0,<br />
(b) t 1 and (c) t 1 4 , 2 .<br />
102. ELECTRIC CIRCUITS The current I (in amperes)<br />
when 100 volts is applied to a circuit is given by<br />
I 5e 2t sin t, where t is the time (in seconds) after<br />
the voltage is applied. Approximate the current at<br />
t 0.7 second after the voltage is applied.<br />
EXPLORATION<br />
Month<br />
January<br />
April<br />
July<br />
October<br />
December<br />
New York<br />
City, N<br />
33<br />
52<br />
77<br />
58<br />
38<br />
Fairbanks,<br />
F<br />
10<br />
32<br />
62<br />
24<br />
6<br />
TRUE OR FALSE? In Exercises 103 and 104, determine<br />
whether the statement is true or false. Justify your answer.<br />
103. In each of the four quadrants, the signs of the secant<br />
function and sine function will be the same.<br />
104. To find the reference angle for an angle (given in<br />
degrees), find the integer n such that<br />
0 360n 360. The difference 360n is<br />
the reference angle.<br />
105. WRITING Consider an angle in standard position<br />
with r 12 centimeters, as shown in the figure. Write<br />
a short paragraph describing the changes in the values<br />
of x, y, sin , cos , and tan as increases<br />
continuously from 0 to 90.<br />
y<br />
<br />
12 cm<br />
107. THINK ABOUT IT The figure shows point Px, y on<br />
a unit circle and right triangle OAP.<br />
(a) Find sin t and cos t using the unit circle definitions<br />
of sine and cosine (from Section 4.2).<br />
(b) What is the value of r? Explain.<br />
θ<br />
(c) Use the definitions of sine and cosine given in <strong>this</strong><br />
section to find sin and cos . Write your answers<br />
in terms of x and y.<br />
<br />
O<br />
y<br />
θ<br />
(d) Based on your answers to parts (a) and (c), what<br />
can you conclude?<br />
r<br />
P(x, y)<br />
A<br />
<br />
t<br />
<br />
(x, y)<br />
106. CAPSTONE Write a short paper in your own words<br />
explaining to a classmate how to evaluate the six<br />
trigonometric functions of any angle in standard<br />
position. Include an explanation of reference angles<br />
and how to use them, the signs of the functions in<br />
each of the four quadrants, and the trigonometric<br />
values of common angles. Be sure to include figures<br />
or diagrams in your paper.<br />
<br />
x<br />
<br />
x
Section 4.5 Graphs of Sine and Cosine Functions 319<br />
4.5 GRAPHS OF SINE AND COSINE FUNCTIONS<br />
What you should learn<br />
• Sketch the graphs of basic sine and<br />
cosine functions.<br />
• Use amplitude and period to help<br />
sketch the graphs of sine and cosine<br />
functions.<br />
• Sketch translations of the graphs<br />
of sine and cosine functions.<br />
• Use sine and cosine functions to<br />
model real-life data.<br />
Why you should learn it<br />
Sine and cosine functions are<br />
often used in scientific calculations.<br />
For instance, in Exercise 87 on page 328,<br />
you can use a trigonometric function<br />
to model the airflow of your<br />
respiratory cycle.<br />
Basic Sine and Cosine Curves<br />
In <strong>this</strong> section, you will study techniques for sketching the graphs of the sine and cosine<br />
functions. The graph of the sine function is a sine curve. In Figure 4.47, the black<br />
portion of the graph represents one period of the function and is called one cycle of the<br />
sine curve. The gray portion of the graph indicates that the basic sine curve repeats<br />
indefinitely in the positive and negative directions. The graph of the cosine function is<br />
shown in Figure 4.48.<br />
Recall from Section 4.2 that the domain of the sine and cosine functions is the set<br />
of all real numbers. Moreover, the range of each function is the interval 1, 1, and<br />
each function has a period of 2. Do you see how <strong>this</strong> information is consistent with<br />
the basic graphs shown in Figures 4.47 and 4.48?<br />
y = sin x<br />
1<br />
y<br />
Range:<br />
−1 ≤ y ≤ 1<br />
− 3 π −π − π π π 3π<br />
2π<br />
5 π<br />
2<br />
2<br />
2<br />
2<br />
2<br />
x<br />
−1<br />
Period: 2π<br />
FIGURE 4.47<br />
y<br />
© Karl Weatherly/Corbis<br />
Range:<br />
−1 ≤ y ≤ 1<br />
1<br />
y = cos x<br />
−<br />
3 π −π π π 3π<br />
2π 5π<br />
2<br />
2<br />
2<br />
2<br />
x<br />
−1<br />
Period: 2π<br />
FIGURE 4.48<br />
Note in Figures 4.47 and 4.48 that the sine curve is symmetric with respect to<br />
the origin, whereas the cosine curve is symmetric with respect to the y-axis. These<br />
properties of symmetry follow from the fact that the sine function is odd and the cosine<br />
function is even.
320 Chapter 4 Trigonometry<br />
To sketch the graphs of the basic sine and cosine functions by hand, it helps to note<br />
five key points in one period of each graph: the intercepts, maximum points, and<br />
minimum points (see Figure 4.49).<br />
y<br />
y<br />
Maximum Intercept Minimum Intercept<br />
Intercept π<br />
( , 1<br />
2 ) y = sin x<br />
(0, 0)<br />
Quarter<br />
period<br />
Half<br />
period<br />
Period: 2π<br />
( π, 0)<br />
3π<br />
( , − 1)<br />
2<br />
Three-quarter<br />
period<br />
(2 π, 0)<br />
Full<br />
period<br />
x<br />
(0, 1)<br />
Intercept Minimum<br />
Maximum<br />
y = cos x<br />
Quarter<br />
period<br />
Period: 2π<br />
π<br />
( , 0<br />
3π<br />
) ( , 0)<br />
2 2<br />
( π, −1)<br />
Half<br />
period<br />
Intercept<br />
(2 π, 1)<br />
Three-quarter<br />
period<br />
Maximum<br />
Full<br />
period<br />
x<br />
FIGURE 4.49<br />
Example 1<br />
Using Key Points to Sketch a Sine Curve<br />
Sketch the graph of y 2 sin x on the interval , 4.<br />
Solution<br />
Note that<br />
y 2 sin x 2sin x<br />
indicates that the y-values for the key points will have twice the magnitude of those on<br />
the graph of y sin x. Divide the period into four equal parts to get the key points<br />
for y 2 sin x.<br />
Intercept Maximum Intercept Minimum Intercept<br />
0, 0,<br />
<br />
<br />
2 , 2 ,<br />
By connecting these key points with a smooth curve and extending the curve in both<br />
directions over the interval , 4, you obtain the graph shown in Figure 4.50.<br />
y<br />
, 0,<br />
2<br />
3<br />
2 , 2 ,<br />
and<br />
2, 0<br />
TECHNOLOGY<br />
When using a graphing utility to<br />
graph trigonometric functions,<br />
pay special attention to the viewing<br />
window you use. For instance,<br />
try graphing y [sin10x]/10<br />
in the standard viewing window<br />
in radian mode. What do you<br />
observe? Use the zoom feature<br />
to find a viewing window that<br />
displays a good view of the graph.<br />
π<br />
−<br />
2<br />
FIGURE 4.50<br />
3<br />
2<br />
1<br />
−2<br />
Now try Exercise 39.<br />
y = 2 sin x<br />
3π<br />
2<br />
5π<br />
y = sin x<br />
2<br />
7π<br />
2<br />
x
Section 4.5 Graphs of Sine and Cosine Functions 321<br />
Amplitude and Period<br />
In the remainder of <strong>this</strong> section you will study the graphic effect of each of the<br />
constants a, b, c, and d in equations of the forms<br />
y d a sinbx c<br />
and<br />
y d a cosbx c.<br />
A quick review of the transformations you studied in Section 1.7 should help in <strong>this</strong><br />
investigation.<br />
The constant factor a in y a sin x acts as a scaling factor—a vertical stretch or<br />
vertical shrink of the basic sine curve. If the basic sine curve is stretched, and<br />
if a a > 1,<br />
< 1, the basic sine curve is shrunk. The result is that the graph of y a sin x<br />
ranges between a and a instead of between 1 and 1. The absolute value of a is the<br />
amplitude of the function y a sin x. The range of the function y a sin x for a > 0<br />
is a y a.<br />
Definition of Amplitude of Sine and Cosine Curves<br />
The amplitude of y a sin x and y a cos x represents half the distance<br />
between the maximum and minimum values of the function and is given by<br />
Amplitude a .<br />
Example 2<br />
Scaling: Vertical Shrinking and Stretching<br />
On the same coordinate axes, sketch the graph of each function.<br />
a. y 1 b.<br />
2 cos x<br />
y 3 cos x<br />
y<br />
3<br />
−1<br />
−2<br />
−3<br />
FIGURE 4.51<br />
y = cos x<br />
y<br />
y = 3 cos x<br />
2π<br />
1<br />
= cos<br />
2<br />
x<br />
x<br />
Solution<br />
a. Because the amplitude of 1<br />
1<br />
2 cos x is 2 , the maximum value is 2 and the minimum<br />
value is 1 2 . Divide one cycle, 0 x 2, into four equal parts to get the key<br />
0, , <br />
2 1 , 2 1 , 3<br />
2 , 0 ,<br />
2 , 0 , and 2, 1 2 .<br />
points<br />
Maximum Intercept Minimum Intercept Maximum<br />
b. A similar analysis shows that the amplitude of y 3 cos x is 3, and the key points<br />
are<br />
Maximum Intercept Minimum Intercept Maximum<br />
0, 3, , 3,<br />
and<br />
<br />
<br />
<br />
2, 3.<br />
2 , 0 ,<br />
The graphs of these two functions are shown in Figure 4.51. Notice that the graph<br />
of y 1 2 cos x is a vertical shrink of the graph of y cos x and the graph of y 3 cos x<br />
is a vertical stretch of the graph of y cos x.<br />
Now try Exercise 41.<br />
3<br />
2 , 0 ,
322 Chapter 4 Trigonometry<br />
y<br />
y = 3 cos x y = −3 cos x<br />
3<br />
1<br />
You know from Section 1.7 that the graph of y f x is a reflection in the<br />
x-axis of the graph of y f x. For instance, the graph of y 3 cos x is a reflection<br />
of the graph of y 3 cos x, as shown in Figure 4.52.<br />
Because y a sin x completes one cycle from x 0 to x 2, it follows that<br />
y a sin bx completes one cycle from x 0 to x 2b.<br />
−π<br />
π<br />
2π<br />
x<br />
Period of Sine and Cosine Functions<br />
Let b be a positive real number. The period of y a sin bx and y a cos bx is<br />
given by<br />
FIGURE 4.52<br />
−3<br />
Period 2<br />
b .<br />
Note that if 0 < b < 1, the period of y a sin bx is greater than and<br />
represents a horizontal stretching of the graph of y a sin x. Similarly, if b > 1, the<br />
period of y a sin bx is less than and represents a horizontal shrinking of the graph<br />
of y a sin x. If b is negative, the identities sinx sin x and cosx cos x<br />
are used to rewrite the function.<br />
2<br />
2<br />
Example 3<br />
Scaling: Horizontal Stretching<br />
Sketch the graph of y sin x 2 .<br />
In general, to divide a<br />
period-interval into four equal<br />
parts, successively add<br />
“period4,”<br />
starting with the<br />
left endpoint of the interval. For<br />
instance, for the period-interval<br />
6, 2 of length 23,<br />
you would successively add<br />
23<br />
4<br />
<br />
<br />
6<br />
to get 6, 0, 6, 3, and<br />
2 as the x-values for the key<br />
points on the graph.<br />
Solution<br />
The amplitude is 1. Moreover, because b 1 2 , the period is<br />
Substitute for b.<br />
Now, divide the period-interval 0, 4 into four equal parts with the values , 2, and<br />
to obtain the key points on the graph.<br />
3<br />
2<br />
b 2<br />
1<br />
4.<br />
2<br />
Intercept Maximum Intercept Minimum Intercept<br />
0, 0, , 1, 2, 0, 3, 1, and 4, 0<br />
The graph is shown in Figure 4.53.<br />
y<br />
y = sin x<br />
1<br />
y = sin x 2<br />
x<br />
−π<br />
π<br />
−1<br />
FIGURE 4.53<br />
Now try Exercise 43.<br />
Period: 4π
Section 4.5 Graphs of Sine and Cosine Functions 323<br />
You can review the techniques<br />
for shifting, reflecting, and<br />
stretching graphs in Section 1.7.<br />
Translations of Sine and Cosine Curves<br />
The constant c in the general equations<br />
y a sinbx c<br />
and<br />
creates a horizontal translation (shift) of the basic sine and cosine curves. Comparing<br />
y a sin bx with y a sinbx c, you find that the graph of y a sinbx c<br />
completes one cycle from bx c 0 to bx c 2. By solving for you can find<br />
the interval for one cycle to be<br />
Left endpoint Right endpoint<br />
c<br />
b x c b 2<br />
y a cosbx c<br />
b . x,<br />
Period<br />
This implies that the period of y a sinbx c is 2b, and the graph of y a sin bx<br />
is shifted by an amount cb. The number cb is the phase shift.<br />
Graphs of Sine and Cosine Functions<br />
The graphs of y a sinbx c and y a cosbx c have the following<br />
characteristics. (Assume b > 0. )<br />
Amplitude<br />
a <br />
Period<br />
2<br />
b<br />
The left and right endpoints of a one-cycle interval can be determined by solving<br />
the equations bx c 0 and bx c 2.<br />
Example 4<br />
Horizontal Translation<br />
Analyze the graph of y 1 2 sin x <br />
Algebraic Solution<br />
<br />
3 .<br />
The amplitude is 2 and the period is 2. By solving the equations<br />
x <br />
x <br />
3 0 3<br />
and<br />
x <br />
3 2<br />
you see that the interval 3, 73 corresponds to one cycle of the<br />
graph. Dividing <strong>this</strong> interval into four equal parts produces the key<br />
points<br />
Intercept Maximum Intercept Minimum Intercept<br />
5<br />
4<br />
11 and 7<br />
6 , 1 3 , 0 , 2 , 3 , 0 , 6 , 1 2 , 3 , 0 .<br />
<br />
<br />
<br />
1<br />
<br />
x 7<br />
3<br />
Now try Exercise 49.<br />
Graphical Solution<br />
Use a graphing utility set in radian mode to graph<br />
y 12 sinx 3, as shown in Figure 4.54.<br />
Use the minimum, maximum, and zero or root<br />
features of the graphing utility to approximate the<br />
key points 1.05, 0, 2.62, 0.5, 4.19, 0,<br />
5.76, 0.5, and 7.33, 0.<br />
−<br />
2<br />
1<br />
−1<br />
FIGURE 4.54<br />
1 π<br />
y = sin<br />
2 ( x −<br />
3<br />
5<br />
2<br />
(
324 Chapter 4 Trigonometry<br />
y = −3 cos(2πx + 4 π)<br />
y<br />
−2<br />
3<br />
2<br />
1<br />
x<br />
Example 5 Horizontal Translation<br />
Sketch the graph of<br />
y 3 cos2x 4.<br />
Solution<br />
The amplitude is 3 and the period is<br />
2x 4 0<br />
22 1.<br />
By solving the equations<br />
2x 4<br />
−3<br />
x 2<br />
Period 1<br />
FIGURE 4.55<br />
and<br />
2x 4 2<br />
2x 2<br />
x 1<br />
you see that the interval 1 corresponds to one cycle of the graph. Dividing <strong>this</strong><br />
interval into four equal parts produces the key points<br />
Minimum Intercept Maximum Intercept Minimum<br />
2,<br />
2, 3,<br />
7 4 , 0 ,<br />
3 2 , 3 ,<br />
5 4 , 0 ,<br />
and<br />
1, 3.<br />
The graph is shown in Figure 4.55.<br />
Now try Exercise 51.<br />
d<br />
The final type of transformation is the vertical translation caused by the constant<br />
in the equations<br />
y d a sinbx c<br />
and<br />
y d a cosbx c.<br />
The shift is d units upward for d > 0 and d units downward for d < 0. In other words,<br />
the graph oscillates about the horizontal line y d instead of about the x-axis.<br />
y<br />
5<br />
y = 2 + 3 cos 2x<br />
Example 6 Vertical Translation<br />
Sketch the graph of<br />
y 2 3 cos 2x.<br />
−π<br />
FIGURE 4.56<br />
1<br />
−1<br />
π<br />
Period π<br />
x<br />
Solution<br />
The amplitude is 3 and the period is . The key points over the interval 0, are<br />
0, 5, 3 and , 5.<br />
4 , 2 , 2 , 1 , 4 , 2 ,<br />
<br />
<br />
The graph is shown in Figure 4.56. Compared with the graph of f x 3 cos 2x, the<br />
graph of y 2 3 cos 2x is shifted upward two units.<br />
Now try Exercise 57.
Section 4.5 Graphs of Sine and Cosine Functions 325<br />
Time, t<br />
Midnight<br />
2 A.M.<br />
4 A.M.<br />
6 A.M.<br />
8 A.M.<br />
10 A.M.<br />
Noon<br />
Depth, y<br />
3.4<br />
8.7<br />
11.3<br />
9.1<br />
3.8<br />
0.1<br />
1.2<br />
Mathematical Modeling<br />
Sine and cosine functions can be used to model many real-life situations, including<br />
electric currents, musical tones, radio waves, tides, and weather patterns.<br />
Example 7<br />
Finding a Trigonometric Model<br />
Throughout the day, the depth of water at the end of a dock in Bar Harbor, Maine varies<br />
with the tides. The table shows the depths (in feet) at various times during the<br />
morning. (Source: Nautical Software, Inc.)<br />
a. Use a trigonometric function to model the data.<br />
b. Find the depths at 9 A.M. and 3 P.M.<br />
c. A boat needs at least 10 feet of water to moor at the dock. During what times in the<br />
afternoon can it safely dock?<br />
Depth (in feet)<br />
12<br />
10<br />
8<br />
6<br />
4<br />
2<br />
y<br />
FIGURE 4.57<br />
12<br />
Changing Tides<br />
4 A.M. 8 A.M. Noon<br />
Time<br />
0 24<br />
0<br />
y = 5.6 cos(0.524t − 2.094) + 5.7<br />
FIGURE 4.58<br />
(14.7, 10) (17.3, 10)<br />
y = 10<br />
t<br />
Solution<br />
a. Begin by graphing the data, as shown in Figure 4.57. You can use either a sine or a<br />
cosine model. Suppose you use a cosine model of the form<br />
y a cosbt c d.<br />
The difference between the maximum height and the minimum height of the graph<br />
is twice the amplitude of the function. So, the amplitude is<br />
a 1 maximum depth minimum depth<br />
2<br />
The cosine function completes one half of a cycle between the times at which the<br />
maximum and minimum depths occur. So, the period is<br />
p 2time of min. depth time of max. depth 210 4 12<br />
which implies that b 2p 0.524. Because high tide occurs 4 hours after<br />
midnight, consider the left endpoint to be cb 4, so c 2.094. Moreover,<br />
1<br />
because the average depth is 2 11.3 0.1 5.7, it follows that d 5.7. So, you<br />
can model the depth with the function given by<br />
y 5.6 cos0.524t 2.094 5.7.<br />
b. The depths at 9 A.M. and 3 P.M. are as follows.<br />
y 5.6 cos0.524 9 2.094 5.7<br />
0.84 foot<br />
y 5.6 cos0.524 15 2.094 5.7<br />
10.57 feet<br />
9 A.M.<br />
3 P.M.<br />
c. To find out when the depth y is at least 10 feet, you can graph the model with the<br />
line y 10 using a graphing utility, as shown in Figure 4.58. Using the intersect<br />
feature, you can determine that the depth is at least 10 feet between 2:42 P.M.<br />
t 14.7 and 5:18 P.M. t 17.3.<br />
Now try Exercise 91.<br />
1 11.3 0.1<br />
2<br />
5.6.
326 Chapter 4 Trigonometry<br />
4.5 EXERCISES<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
VOCABULARY: Fill in the blanks.<br />
1. One period of a sine or cosine function is called one ________ of the sine or cosine curve.<br />
2. The ________ of a sine or cosine curve represents half the distance between the maximum and minimum values<br />
of the function.<br />
c<br />
3. For the function given by y a sinbx c, represents the ________ ________ of the graph of the function.<br />
b<br />
4. For the function given by y d a cosbx c, d represents a ________ ________ of the graph of the function.<br />
SKILLS AND APPLICATIONS<br />
In Exercises 5–18, find the period and amplitude.<br />
5. y 2 sin 5x<br />
6. y 3 cos 2x<br />
3<br />
2<br />
1<br />
−3<br />
1<br />
−1<br />
1<br />
−1<br />
y<br />
y<br />
y<br />
π<br />
10<br />
π 2π<br />
9. y 1 10. y 3 2 sin x<br />
3<br />
2 cos<br />
π<br />
2<br />
11. y 4 sin x 12.<br />
y<br />
13. y 3 sin 10x 14. y 1 5 sin 6x<br />
15. y 5 4x<br />
cos<br />
3 5<br />
16. y 5 2 cos x 4<br />
17. 18. y 2 3 cos x<br />
y 1 sin 2x<br />
4 10<br />
x<br />
x<br />
x<br />
−π<br />
−2<br />
−3<br />
7. y 3 8. y 3 sin x 4 cos x 2<br />
3<br />
4<br />
−π<br />
−2<br />
−4<br />
2<br />
−2<br />
y<br />
y<br />
y<br />
π<br />
cos 2x<br />
3<br />
π<br />
2<br />
x<br />
2<br />
π<br />
x<br />
x<br />
x<br />
In Exercises 19–26, describe the relationship between the<br />
graphs of f and g. Consider amplitude, period, and shifts.<br />
19. f x sin x<br />
20. f x cos x<br />
gx sinx gx cosx <br />
21. f x cos 2x 22. f x sin 3x<br />
gx cos 2x<br />
gx sin3x<br />
23. f x cos x<br />
24. f x sin x<br />
gx cos 2x<br />
gx sin 3x<br />
25. f x sin 2x 26. f x cos 4x<br />
gx 3 sin 2x gx 2 cos 4x<br />
In Exercises 27–30, describe the relationship between the<br />
graphs of f and g. Consider amplitude, period, and shifts.<br />
27. 28.<br />
29. 30.<br />
−2π<br />
3<br />
−2<br />
−3<br />
3<br />
2<br />
1<br />
−2<br />
−3<br />
y<br />
y<br />
2π<br />
In Exercises 31–38, graph f and g on the same set of<br />
coordinate axes. (Include two full periods.)<br />
31. f x 2 sin x 32. f x sin x<br />
gx 4 sin x<br />
f<br />
f<br />
π<br />
g<br />
g<br />
x<br />
x<br />
−2π<br />
gx sin x 3<br />
2π<br />
33. f x cos x<br />
34. f x 2 cos 2x<br />
gx 2 cos x gx cos 4x<br />
g<br />
3<br />
2<br />
−2<br />
−3<br />
4<br />
3<br />
2<br />
−2<br />
y<br />
y<br />
g<br />
f<br />
f<br />
π<br />
x<br />
x
Section 4.5 Graphs of Sine and Cosine Functions 327<br />
35. f x 1 36. f x 4 sin x<br />
2 sin x 2<br />
In Exercises 61–66, g is related to a parent function<br />
fx sinx or fx cosx. (a) Describe the sequence of<br />
transformations from f to g. (b) Sketch the graph of g. (c) Use<br />
function notation to write g in terms of f.<br />
In Exercises 67–72, use a graphing utility to graph the<br />
function. Include two full periods. Be sure to choose an<br />
appropriate viewing window.<br />
67. y 2 sin4x 68.<br />
69.<br />
gx 3 1 2 sin x 2<br />
45. y cos 2x<br />
46. y sin<br />
10<br />
<br />
2<br />
y cos 2x <br />
<br />
4<br />
<br />
70. y 3 cos <br />
x<br />
2 2 2<br />
x<br />
71. y 0.1 sin 72.<br />
10 <br />
<br />
gx 4 sin x 3<br />
<br />
37. f x 2 cos x 38. f x cos x<br />
gx 2 cosx gx cosx<br />
39. y 5 sin x 40. y 1 4 sin x<br />
In Exercises 39– 60, sketch the graph of the function. (Include<br />
two full periods.)<br />
41. y 1 3 cos x<br />
42. y 4 cos x<br />
43. y cos x 44. y sin 4x<br />
2<br />
57. y 3 cosx 3 58. y 4 cos x <br />
4 4<br />
61. gx sin4x 62. gx sin2x <br />
63. gx cosx 2 64. gx 1 cosx <br />
65. gx 2 sin4x 3 66. gx 4 sin2x <br />
x<br />
4<br />
47. y sin 2x 48. y 10 cos<br />
3<br />
51. y 3 cosx 52. y 4 cos x <br />
2 1 y 4 sin <br />
2<br />
x<br />
6<br />
49. y sin x <br />
50. y sinx 2<br />
t<br />
53. y 2 sin 2x 54. y 3 5 cos<br />
3<br />
12<br />
55. y 2 1 cos 60x 56. y 2 cos x 3<br />
59. y 2 60. y 3 cos6x <br />
3 cos x 2 <br />
<br />
4<br />
<br />
3 x <br />
y 1 sin 120t<br />
100<br />
<br />
3<br />
GRAPHICAL REASONING In Exercises 73–76, find a and<br />
d for the function f x a cos x d such that the graph of<br />
f matches the figure.<br />
73. 74.<br />
75. 76.<br />
10<br />
8<br />
6<br />
4<br />
−π −2<br />
GRAPHICAL REASONING In Exercises 77–80, find a, b,<br />
and c for the function f x a sinbx c such that the<br />
graph of f matches the figure.<br />
77. 78.<br />
79. 80.<br />
f<br />
f<br />
4<br />
1<br />
−1<br />
−2<br />
1<br />
−3<br />
3<br />
2<br />
1<br />
−2<br />
−3<br />
In Exercises 81 and 82, use a graphing utility to graph y 1 and<br />
y 2 in the interval [2, 2]. Use the graphs to find real<br />
numbers x such that y 1 y 2 .<br />
81. y 1 sin x<br />
82. y 1 cos x<br />
y 2 1 2<br />
y<br />
y<br />
y<br />
y<br />
π<br />
2<br />
π<br />
π<br />
π<br />
f<br />
f<br />
x<br />
x<br />
x<br />
x<br />
−π<br />
−π<br />
−π<br />
−3<br />
−4<br />
y 2 1<br />
In Exercises 83–86, write an equation for the function that is<br />
described by the given characteristics.<br />
83. A sine curve with a period of , an amplitude of 2,<br />
a right phase shift of 2, and a vertical translation up<br />
1 unit<br />
2<br />
1<br />
−1<br />
−2<br />
−5<br />
3<br />
2<br />
1<br />
−3<br />
3<br />
2<br />
−2<br />
−3<br />
y<br />
y<br />
y<br />
y<br />
π<br />
π<br />
f<br />
π<br />
f<br />
f<br />
f<br />
2 4<br />
x<br />
x<br />
x<br />
x
328 Chapter 4 Trigonometry<br />
84. A sine curve with a period of 4, an amplitude of 3,<br />
a left phase shift of 4, and a vertical translation down<br />
1 unit<br />
85. A cosine curve with a period of , an amplitude of 1,<br />
a left phase shift of , and a vertical translation down<br />
units<br />
3<br />
2<br />
86. A cosine curve with a period of 4, an amplitude of 3,<br />
a right phase shift of 2, and a vertical translation up<br />
2 units<br />
87. RESPIRATORY CYCLE For a person at rest, the velocity<br />
v (in liters per second) of airflow during a respiratory<br />
cycle (the time from the beginning of one breath<br />
to the beginning of the next) is given by<br />
t<br />
v 0.85 sin where t is the time (in seconds). (Inhalation<br />
3 ,<br />
occurs when v > 0, and exhalation occurs when v < 0. )<br />
(a) Find the time for one full respiratory cycle.<br />
(b) Find the number of cycles per minute.<br />
(c) Sketch the graph of the velocity function.<br />
88. RESPIRATORY CYCLE After exercising for a<br />
few minutes, a person has a respiratory cycle for<br />
which the velocity of airflow is approximated<br />
t<br />
by v 1.75 sin where t is the time (in seconds).<br />
2 ,<br />
(Inhalation occurs when v > 0, and exhalation occurs<br />
when v < 0. )<br />
(a) Find the time for one full respiratory cycle.<br />
(b) Find the number of cycles per minute.<br />
(c) Sketch the graph of the velocity function.<br />
89. DATA ANALYSIS: METEOROLOGY The table shows<br />
the maximum daily high temperatures in Las Vegas L<br />
and International Falls I (in degrees Fahrenheit) for<br />
month t, with t 1 corresponding to January. (Source:<br />
National Climatic Data Center)<br />
Month, t Las Vegas, L International Falls, I<br />
1<br />
2<br />
3<br />
4<br />
5<br />
6<br />
7<br />
8<br />
9<br />
10<br />
11<br />
12<br />
57.1<br />
63.0<br />
69.5<br />
78.1<br />
87.8<br />
98.9<br />
104.1<br />
101.8<br />
93.8<br />
80.8<br />
66.0<br />
57.3<br />
13.8<br />
22.4<br />
34.9<br />
51.5<br />
66.6<br />
74.2<br />
78.6<br />
76.3<br />
64.7<br />
51.7<br />
32.5<br />
18.1<br />
(a) A model for the temperature in Las Vegas is given<br />
by<br />
t<br />
Lt 80.60 23.50 cos <br />
6 3.67 .<br />
Find a trigonometric model for International Falls.<br />
(b) Use a graphing utility to graph the data points and<br />
the model for the temperatures in Las Vegas. How<br />
well does the model fit the data?<br />
(c) Use a graphing utility to graph the data points and<br />
the model for the temperatures in International<br />
Falls. How well does the model fit the data?<br />
(d) Use the models to estimate the average maximum<br />
temperature in each city. Which term of the models<br />
did you use? Explain.<br />
(e) What is the period of each model? Are the periods<br />
what you expected? Explain.<br />
(f) Which city has the greater variability in<br />
temperature throughout the year? Which factor<br />
of the models determines <strong>this</strong> variability? Explain.<br />
90. HEALTH The function given by<br />
P 100 20 cos 5t<br />
3<br />
approximates the blood pressure P (in millimeters of<br />
mercury) at time t (in seconds) for a person at rest.<br />
(a) Find the period of the function.<br />
(b) Find the number of heartbeats per minute.<br />
91. PIANO TUNING When tuning a piano, a technician<br />
strikes a tuning fork for the A above middle C and sets<br />
up a wave motion that can be approximated by<br />
y 0.001 sin 880t, where t is the time (in seconds).<br />
(a) What is the period of the function?<br />
(b) The frequency f is given by f 1p. What is the<br />
frequency of the note?<br />
92. DATA ANALYSIS: ASTRONOMY The percents y (in<br />
decimal form) of the moon’s face that was illuminated<br />
on day x in the year 2009, where x 1 represents<br />
January 1, are shown in the table. (Source: U.S. Naval<br />
Observatory)x<br />
x<br />
4<br />
11<br />
18<br />
26<br />
33<br />
40<br />
y<br />
0.5<br />
1.0<br />
0.5<br />
0.0<br />
0.5<br />
1.0
Section 4.5 Graphs of Sine and Cosine Functions 329<br />
(a) Create a scatter plot of the data.<br />
(b) Find a trigonometric model that fits the data.<br />
(c) Add the graph of your model in part (b) to the<br />
scatter plot. How well does the model fit the data?<br />
(d) What is the period of the model?<br />
(e) Estimate the moon’s percent illumination for<br />
March 12, 2009.<br />
93. FUEL CONSUMPTION The daily consumption C (in<br />
gallons) of diesel fuel on a farm is modeled by<br />
C 30.3 21.6 sin <br />
2t<br />
365 10.9 <br />
where t is the time (in days), with t 1 corresponding<br />
to January 1.<br />
(a) What is the period of the model? Is it what you<br />
expected? Explain.<br />
(b) What is the average daily fuel consumption? Which<br />
term of the model did you use? Explain.<br />
(c) Use a graphing utility to graph the model. Use the<br />
graph to approximate the time of the year when<br />
consumption exceeds 40 gallons per day.<br />
94. FERRIS WHEEL A Ferris wheel is built such that the<br />
height h (in feet) above ground of a seat on the wheel at<br />
time t (in seconds) can be modeled by<br />
(a) Find the period of the model. What does the period<br />
tell you about the ride?<br />
(b) Find the amplitude of the model. What does the<br />
amplitude tell you about the ride?<br />
(c) Use a graphing utility to graph one cycle of the<br />
model.<br />
EXPLORATION<br />
<br />
ht 53 50 sin 10 t <br />
TRUE OR FALSE? In Exercises 95–97, determine whether<br />
the statement is true or false. Justify your answer.<br />
95. The graph of the function given by f x sinx 2<br />
translates the graph of f x sin x exactly one period<br />
to the right so that the two graphs look identical.<br />
96. The function given by y 1 2 cos 2x has an amplitude<br />
that is twice that of the function given by y cos x.<br />
97. The graph of y cos x is a reflection of the graph of<br />
y sinx 2 in the x-axis.<br />
98. WRITING Sketch the graph of y cos bx for b 1 2,<br />
2, and 3. How does the value of b affect the graph? How<br />
many complete cycles occur between 0 and for each<br />
value of b?<br />
<br />
2 .<br />
2<br />
99. WRITING Sketch the graph of y sinx c for<br />
c 4, 0, and 4. How does the value of c affect<br />
the graph?<br />
100. CAPSTONE Use a graphing utility to graph the<br />
function given by y d a sinbx c, for several<br />
different values of a, b, c, and d. Write a paragraph<br />
describing the changes in the graph corresponding to<br />
changes in each constant.<br />
CONJECTURE In Exercises 101 and 102, graph f and g on<br />
the same set of coordinate axes. Include two full periods.<br />
Make a conjecture about the functions.<br />
101.<br />
102.<br />
f x sin x, gx cos x <br />
f x sin x, gx cos x <br />
103. Using calculus, it can be shown that the sine and cosine<br />
functions can be approximated by the polynomials<br />
sin x x x3<br />
3! x5<br />
5!<br />
where x is in radians.<br />
and<br />
cos x 1 x 2<br />
(a) Use a graphing utility to graph the sine function<br />
and its polynomial approximation in the same<br />
viewing window. How do the graphs compare?<br />
(b) Use a graphing utility to graph the cosine function<br />
and its polynomial approximation in the same<br />
viewing window. How do the graphs compare?<br />
(c) Study the patterns in the polynomial approximations<br />
of the sine and cosine functions and predict<br />
the next term in each. Then repeat parts (a) and (b).<br />
How did the accuracy of the approximations<br />
change when an additional term was added?<br />
104. Use the polynomial approximations of the sine and<br />
cosine functions in Exercise 103 to approximate<br />
the following function values. Compare the results<br />
with those given by a calculator. Is the error in the<br />
approximation the same in each case? Explain.<br />
(a) sin 1 (b) sin 1 (c) sin<br />
2<br />
6<br />
(d) cos0.5 (e) cos 1 (f) cos<br />
4<br />
<strong>PRO</strong>JECT: METEOROLOGY To work an extended<br />
application analyzing the mean monthly temperature and<br />
mean monthly precipitation in Honolulu, Hawaii, visit <strong>this</strong><br />
text’s website at academic.cengage.com. (Data Source:<br />
National Climatic Data Center)<br />
<br />
2<br />
<br />
2<br />
<br />
<br />
2! x4<br />
4!
330 Chapter 4 Trigonometry<br />
4.6 GRAPHS OF OTHER TRIGONOMETRIC FUNCTIONS<br />
What you should learn<br />
• Sketch the graphs of tangent<br />
functions.<br />
• Sketch the graphs of cotangent<br />
functions.<br />
• Sketch the graphs of secant and<br />
cosecant functions.<br />
• Sketch the graphs of damped<br />
trigonometric functions.<br />
Why you should learn it<br />
Graphs of trigonometric functions can<br />
be used to model real-life situations<br />
such as the distance from a television<br />
camera to a unit in a parade, as in<br />
Exercise 92 on page 339.<br />
Graph of the Tangent Function<br />
Recall that the tangent function is odd. That is, tanx tan x. Consequently, the<br />
graph of y tan x is symmetric with respect to the origin. You also know from the<br />
identity tan x sin xcos x that the tangent is undefined for values at which cos x 0.<br />
Two such values are x ±2 ±1.5708.<br />
x<br />
<br />
<br />
2<br />
tan x Undef. 1255.8 14.1 1 0 1 14.1 1255.8 Undef.<br />
As indicated in the table, tan x increases without bound as x approaches 2 from the<br />
left, and decreases without bound as x approaches 2 from the right. So, the graph<br />
of y tan x has vertical asymptotes at x 2 and x 2, as shown in<br />
Figure 4.59. Moreover, because the period of the tangent function is , vertical<br />
asymptotes also occur when x 2 n, where n is an integer. The domain of the<br />
tangent function is the set of all real numbers other than x 2 n, and the range<br />
is the set of all real numbers.<br />
<br />
1.57 1.5 <br />
4<br />
0<br />
<br />
4<br />
1.5 1.57<br />
<br />
2<br />
Alan Pappe/Photodisc/Getty Images<br />
π<br />
−<br />
3<br />
2<br />
−<br />
π<br />
2<br />
y<br />
3<br />
2<br />
1<br />
π<br />
2<br />
y = tan x<br />
π<br />
3π<br />
2<br />
x<br />
<br />
PERIOD:<br />
DOMAIN: ALL<br />
x 2 n<br />
RANGE: ( , )<br />
x 2 n<br />
<br />
VERTICAL ASYMPTOTES:<br />
SYMMETRY: ORIGIN<br />
<br />
−3<br />
• You can review odd and even<br />
functions in Section 1.5.<br />
• You can review symmetry of<br />
a graph in Section 1.2.<br />
• You can review trigonometric<br />
identities in Section 4.3.<br />
• You can review asymptotes in<br />
Section 2.6.<br />
• You can review domain and<br />
range of a function in Section<br />
1.4.<br />
• You can review intercepts of<br />
a graph in Section 1.2.<br />
FIGURE 4.59<br />
Sketching the graph of y a tanbx c is similar to sketching the graph of<br />
y a sinbx c in that you locate key points that identify the intercepts and asymptotes.<br />
Two consecutive vertical asymptotes can be found by solving the equations<br />
<br />
bx c 2<br />
and<br />
bx c <br />
2 .<br />
The midpoint between two consecutive vertical asymptotes is an x-intercept of the<br />
graph. The period of the function y a tanbx c is the distance between two<br />
consecutive vertical asymptotes. The amplitude of a tangent function is not defined.<br />
After plotting the asymptotes and the x-intercept, plot a few additional points between<br />
the two asymptotes and sketch one cycle. Finally, sketch one or two additional cycles<br />
to the left and right.
Section 4.6 Graphs of Other Trigonometric Functions 331<br />
y<br />
y = tan x 2<br />
Example 1<br />
Sketching the Graph of a Tangent Function<br />
3<br />
Sketch the graph of y tanx2.<br />
−π<br />
2<br />
1<br />
π<br />
3π<br />
x<br />
Solution<br />
By solving the equations<br />
<br />
x<br />
2 2<br />
and<br />
x<br />
2 <br />
<br />
2<br />
x <br />
x <br />
FIGURE 4.60<br />
−3<br />
you can see that two consecutive vertical asymptotes occur at x and x .<br />
Between these two asymptotes, plot a few points, including the x-intercept, as shown in<br />
the table. Three cycles of the graph are shown in Figure 4.60.<br />
x <br />
<br />
<br />
2<br />
0<br />
<br />
2<br />
<br />
tan x 2<br />
Undef. 1 0 1 Undef.<br />
Now try Exercise 15.<br />
Example 2<br />
Sketching the Graph of a Tangent Function<br />
Sketch the graph of y 3 tan 2x.<br />
6<br />
y<br />
y = −3 tan 2x<br />
Solution<br />
By solving the equations<br />
<br />
2x <br />
2<br />
and<br />
<br />
2x <br />
2<br />
−<br />
3π<br />
4<br />
−<br />
π<br />
2<br />
−<br />
π<br />
4<br />
−2<br />
−4<br />
π π 3π<br />
4 2 4<br />
x<br />
<br />
x <br />
4<br />
<br />
x <br />
4<br />
you can see that two consecutive vertical asymptotes occur at x 4 and x 4.<br />
Between these two asymptotes, plot a few points, including the x-intercept, as shown in<br />
the table. Three cycles of the graph are shown in Figure 4.61.<br />
−6<br />
FIGURE 4.61 x <br />
4<br />
<br />
<br />
<br />
8<br />
0<br />
<br />
<br />
8 4<br />
3 tan 2x Undef. 3 0 3 Undef.<br />
By comparing the graphs in Examples 1 and 2, you can see that the graph of<br />
y a tanbx c increases between consecutive vertical asymptotes when a > 0, and<br />
decreases between consecutive vertical asymptotes when a < 0. In other words, the graph<br />
for a < 0 is a reflection in the x-axis of the graph for a > 0.<br />
Now try Exercise 17.
332 Chapter 4 Trigonometry<br />
TECHNOLOGY<br />
Some graphing utilities have<br />
difficulty graphing trigonometric<br />
functions that have vertical<br />
asymptotes. Your graphing utility<br />
may connect parts of the graphs<br />
of tangent, cotangent, secant,<br />
and cosecant functions that are<br />
not supposed to be connected.<br />
To eliminate <strong>this</strong> problem,<br />
change the mode of the graphing<br />
utility to dot mode.<br />
Graph of the Cotangent Function<br />
The graph of the cotangent function is similar to the graph of the tangent function. It<br />
also has a period of . However, from the identity<br />
y cot x cos x<br />
sin x<br />
you can see that the cotangent function has vertical asymptotes when sin x is zero,<br />
which occurs at x n, where n is an integer. The graph of the cotangent function is<br />
shown in Figure 4.62. Note that two consecutive vertical asymptotes of the graph of<br />
y a cotbx c can be found by solving the equations bx c 0 and bx c .<br />
−π<br />
−<br />
π<br />
2<br />
3<br />
2<br />
1<br />
y<br />
y = cot x<br />
π<br />
2<br />
π<br />
3π<br />
2<br />
2π<br />
x<br />
<br />
PERIOD:<br />
DOMAIN: ALL<br />
x n<br />
RANGE: ( , )<br />
x n<br />
VERTICAL ASYMPTOTES:<br />
SYMMETRY: ORIGIN<br />
FIGURE 4.62<br />
y<br />
y = 2 cot<br />
x<br />
3<br />
Example 3<br />
Sketching the Graph of a Cotangent Function<br />
3<br />
2<br />
1<br />
−2π π 3π 4π<br />
6π<br />
FIGURE 4.63<br />
x<br />
Sketch the graph of<br />
Solution<br />
By solving the equations<br />
y 2 cot x 3 .<br />
x<br />
x<br />
and<br />
3 0 3 3<br />
x 0<br />
x 3<br />
you can see that two consecutive vertical asymptotes occur at x 0 and x 3.<br />
Between these two asymptotes, plot a few points, including the x-intercept, as shown in<br />
the table. Three cycles of the graph are shown in Figure 4.63. Note that the period is<br />
3, the distance between consecutive asymptotes.<br />
x 0<br />
3<br />
4<br />
3<br />
2<br />
9<br />
4<br />
3<br />
2 cot x 3<br />
Undef. 2 0 2 Undef.<br />
Now try Exercise 27.
Section 4.6 Graphs of Other Trigonometric Functions 333<br />
Graphs of the Reciprocal Functions<br />
The graphs of the two remaining trigonometric functions can be obtained from the<br />
graphs of the sine and cosine functions using the reciprocal identities<br />
csc x 1<br />
sin x<br />
and<br />
For instance, at a given value of x, the y-coordinate of sec x is the reciprocal of the<br />
y-coordinate of cos x. Of course, when cos x 0, the reciprocal does not exist. Near<br />
such values of x, the behavior of the secant function is similar to that of the tangent<br />
function. In other words, the graphs of<br />
tan x sin x<br />
cos x<br />
and<br />
have vertical asymptotes at x 2 n, where n is an integer, and the cosine is zero<br />
at these x-values. Similarly,<br />
cot x cos x<br />
sin x<br />
and<br />
sec x 1<br />
cos x .<br />
sec x 1<br />
cos x<br />
csc x 1<br />
sin x<br />
have vertical asymptotes where sin x 0—that is, at x n.<br />
To sketch the graph of a secant or cosecant function, you should first make a sketch<br />
of its reciprocal function. For instance, to sketch the graph of y csc x, first sketch the<br />
graph of y sin x. Then take reciprocals of the y-coordinates to obtain points on the<br />
graph of y csc x. This procedure is used to obtain the graphs shown in Figure 4.64.<br />
y<br />
y<br />
3<br />
y = csc x<br />
3<br />
y = sec x<br />
y = sin x<br />
2<br />
−π<br />
−1<br />
π<br />
2<br />
π<br />
x<br />
−π<br />
−1<br />
−2<br />
π<br />
2<br />
π<br />
x<br />
2π<br />
y = cos x<br />
−3<br />
4<br />
3<br />
2<br />
1<br />
−1<br />
−2<br />
−3<br />
−4<br />
y<br />
Sine: π<br />
maximum<br />
Cosecant:<br />
relative<br />
maximum<br />
FIGURE 4.65<br />
Cosecant:<br />
relative<br />
minimum<br />
Sine:<br />
minimum<br />
2π<br />
x<br />
2<br />
PERIOD:<br />
DOMAIN: ALL<br />
x n<br />
RANGE: ( , 1 1, )<br />
x n<br />
VERTICAL ASYMPTOTES:<br />
SYMMETRY: ORIGIN<br />
FIGURE 4.64<br />
PERIOD:<br />
DOMAIN: ALL<br />
x 2 n<br />
RANGE: ( , 1 1, )<br />
VERTICAL ASYMPTOTES: x 2 n<br />
SYMMETRY: y-AXIS<br />
In comparing the graphs of the cosecant and secant functions with those of the sine<br />
and cosine functions, note that the “hills” and “valleys” are interchanged. For example,<br />
a hill (or maximum point) on the sine curve corresponds to a valley (a relative<br />
minimum) on the cosecant curve, and a valley (or minimum point) on the sine curve<br />
corresponds to a hill (a relative maximum) on the cosecant curve, as shown in<br />
Figure 4.65. Additionally, x-intercepts of the sine and cosine functions become vertical<br />
asymptotes of the cosecant and secant functions, respectively (see Figure 4.65).<br />
2
334 Chapter 4 Trigonometry<br />
y = 2 csc x +<br />
π<br />
4<br />
FIGURE 4.66<br />
( )<br />
y<br />
y = 2 sin x +<br />
π<br />
( 4 )<br />
4<br />
3<br />
1<br />
π<br />
2π<br />
x<br />
Example 4<br />
Sketching the Graph of a Cosecant Function<br />
Sketch the graph of y 2 csc x <br />
Solution<br />
Begin by sketching the graph of<br />
y 2 sin x <br />
For <strong>this</strong> function, the amplitude is 2 and the period is 2. By solving the equations<br />
x <br />
and x <br />
4 0 4 2<br />
<br />
<br />
x <br />
4<br />
you can see that one cycle of the sine function corresponds to the interval from<br />
x 4 to x 74. The graph of <strong>this</strong> sine function is represented by the gray<br />
curve in Figure 4.66. Because the sine function is zero at the midpoint and endpoints of<br />
<strong>this</strong> interval, the corresponding cosecant function<br />
y 2 csc x <br />
<br />
4 .<br />
<br />
4<br />
2 <br />
1<br />
sinx 4<br />
has vertical asymptotes at x 4, x 34, x 74, etc. The graph of the<br />
cosecant function is represented by the black curve in Figure 4.66.<br />
Now try Exercise 33.<br />
<br />
4 .<br />
<br />
x 7<br />
4<br />
Example 5<br />
Sketching the Graph of a Secant Function<br />
Sketch the graph of y sec 2x.<br />
y = sec 2x<br />
−π<br />
−<br />
π<br />
2<br />
y<br />
3<br />
−1<br />
−2<br />
−3<br />
y = cos 2x<br />
π<br />
2<br />
π<br />
x<br />
Solution<br />
Begin by sketching the graph of y cos 2x, as indicated by the gray curve in Figure<br />
4.67. Then, form the graph of y sec 2x as the black curve in the figure. Note that the<br />
x-intercepts of y cos 2x<br />
3<br />
4 , 0 , 4 , 0 , 4 , 0 , . . .<br />
correspond to the vertical asymptotes<br />
x x x 3<br />
4 , 4 , 4 , . . .<br />
<br />
<br />
<br />
<br />
of the graph of y sec 2x. Moreover, notice that the period of y cos 2x and<br />
y sec 2x is .<br />
FIGURE 4.67<br />
Now try Exercise 35.
Section 4.6 Graphs of Other Trigonometric Functions 335<br />
y<br />
y = −x 3π<br />
2π<br />
π<br />
y = x<br />
π<br />
−π<br />
−2π<br />
−3π<br />
f(x) = x sin x<br />
FIGURE 4.68<br />
x<br />
Damped Trigonometric Graphs<br />
A product of two functions can be graphed using properties of the individual functions.<br />
For instance, consider the function<br />
as the product of the functions y x and y sin x. Using properties of absolute value<br />
and the fact that sin x 1, you have 0 xsin x x. Consequently,<br />
which means that the graph of f x x sin x lies between the lines y x and y x.<br />
Furthermore, because<br />
and<br />
f x x sin x<br />
x x sin x x <br />
f x x sin x ±x<br />
f x x sin x 0<br />
at<br />
at<br />
<br />
x <br />
2 n<br />
x n<br />
the graph of f touches the line y x or the line y x at x 2 n and has<br />
x-intercepts at x n. A sketch of f is shown in Figure 4.68. In the function<br />
f x x sin x, the factor x is called the damping factor.<br />
Example 6<br />
Damped Sine Wave<br />
Do you see why the graph of<br />
f x x sin x touches the lines<br />
y ±x at x 2 n and<br />
why the graph has x-intercepts<br />
at x n? Recall that the sine<br />
function is equal to 1 at 2,<br />
32, 52, . . . odd multiples<br />
of 2 and is equal to 0 at ,<br />
2, 3, . . . multiples of .<br />
f(x) = e −x sin 3x y<br />
6<br />
4<br />
y = e −x<br />
x<br />
π 2π<br />
π<br />
3 3<br />
y = −e −x<br />
−4<br />
−6<br />
Sketch the graph of f x e x sin 3x.<br />
Solution<br />
Consider f x as the product of the two functions<br />
and<br />
each of which has the set of real numbers as its domain. For any real number x, you<br />
know that e x 0 and So, e x sin 3x e x , which means that<br />
Furthermore, because<br />
and<br />
y e x<br />
e x e x sin 3x e x .<br />
f x e x sin 3x ±e x<br />
f x e x sin 3x 0<br />
y sin 3x<br />
sin 3x 1.<br />
at<br />
at<br />
the graph of f touches the curves y e x and y e x at x 6 n3 and has<br />
intercepts at x n3. A sketch is shown in Figure 4.69.<br />
Now try Exercise 65.<br />
x <br />
6 n<br />
3<br />
x n<br />
3<br />
<br />
FIGURE 4.69
336 Chapter 4 Trigonometry<br />
Figure 4.70 summarizes the characteristics of the six basic trigonometric functions.<br />
y<br />
y<br />
y<br />
y = tan x<br />
−π<br />
−<br />
π<br />
2<br />
2<br />
1<br />
y = sin x<br />
π π 3π<br />
2 2<br />
x<br />
2<br />
y = cos x<br />
−π<br />
π 2π<br />
−1<br />
x<br />
−<br />
π<br />
2<br />
3<br />
2<br />
1<br />
π<br />
2<br />
π<br />
3π<br />
2<br />
5π<br />
2<br />
x<br />
−2<br />
−2<br />
DOMAIN: ( , )<br />
1, 1<br />
RANGE:<br />
PERIOD: 2<br />
DOMAIN: ( , )<br />
1, 1<br />
RANGE:<br />
PERIOD: 2<br />
DOMAIN: ALL x 2 n<br />
RANGE: ( , )<br />
PERIOD:<br />
<br />
<br />
3<br />
y<br />
y = csc x =<br />
1<br />
sin x<br />
y<br />
3<br />
y = sec x =<br />
1<br />
cos x<br />
y<br />
3<br />
y = cot x =<br />
1<br />
tan x<br />
2<br />
2<br />
1<br />
1<br />
−π π π 2π<br />
2<br />
x<br />
−π<br />
− π 2<br />
π<br />
2<br />
π<br />
3π<br />
2<br />
2π<br />
x<br />
π<br />
2π<br />
x<br />
−2<br />
−3<br />
DOMAIN: ALL x n<br />
RANGE: ( , 1 1, )<br />
PERIOD:<br />
2<br />
FIGURE 4.70<br />
DOMAIN: ALL x 2 n<br />
RANGE: ( , 1 1, )<br />
PERIOD: 2<br />
<br />
DOMAIN: ALL x n<br />
RANGE: ( , )<br />
PERIOD:<br />
<br />
CLASSROOM DISCUSSION<br />
Combining Trigonometric Functions Recall from Section 1.8 that functions can<br />
be combined arithmetically. This also applies to trigonometric functions. For each of<br />
the functions<br />
hx x sin x<br />
and<br />
(a) identify two simpler functions f and g that comprise the combination, (b) use a<br />
table to show how to obtain the numerical values of hx from the numerical values<br />
of fx and gx, and (c) use graphs of f and g to show how the graph of h may be<br />
formed.<br />
Can you find functions<br />
fx d a sinbx c<br />
such that fx gx 0 for all x?<br />
hx cos x sin 3x<br />
and<br />
gx d a cosbx c
Section 4.6 Graphs of Other Trigonometric Functions 337<br />
4.6<br />
EXERCISES<br />
VOCABULARY: Fill in the blanks.<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
1. The tangent, cotangent, and cosecant functions are ________ , so the graphs of these functions have symmetry<br />
with respect to the ________.<br />
2. The graphs of the tangent, cotangent, secant, and cosecant functions all have ________ asymptotes.<br />
3. To sketch the graph of a secant or cosecant function, first make a sketch of its corresponding ________ function.<br />
4. For the functions given by f x gx sin x, gx is called the ________ factor of the function f x.<br />
5. The period of y tan x is ________.<br />
6. The domain of y cot x is all real numbers such that ________.<br />
7. The range of y sec x is ________.<br />
8. The period of y csc x is ________.<br />
SKILLS AND APPLICATIONS<br />
In Exercises 9–14, match the function with its graph. State<br />
the period of the function. [The graphs are labeled (a), (b),<br />
(c), (d), (e), and (f).]<br />
(a)<br />
2<br />
1<br />
y<br />
1<br />
x<br />
(b)<br />
1<br />
y<br />
2<br />
x<br />
In Exercises 15–38, sketch the graph of the function. Include<br />
two full periods.<br />
15. y 1 16. y tan 4x<br />
3 tan x<br />
17. y 2 tan 3x 18. y 3 tan x<br />
19. 2 sec x 20. y 1 4 sec x<br />
21. y csc x<br />
22. y 3 csc 4x<br />
23. y 1 2 sec x<br />
24. y 2 sec 4x 2<br />
(c)<br />
(e)<br />
−<br />
3π<br />
2<br />
4<br />
3<br />
2<br />
1<br />
−3<br />
−4<br />
4<br />
y<br />
y<br />
π<br />
2<br />
π<br />
2<br />
x<br />
x<br />
(d)<br />
(f)<br />
y<br />
3<br />
2<br />
π 3π<br />
−<br />
2 2<br />
−3<br />
y<br />
3<br />
1<br />
x<br />
x<br />
25. y csc x 26. y csc x 2<br />
3<br />
27. y 3 cot 2x<br />
28.<br />
y<br />
29. y 2 sec 3x<br />
30. y 1 2 tan x<br />
x<br />
31. y tan<br />
4<br />
32. y tanx <br />
33. y 2 cscx 34. y csc2x <br />
35. y 2 secx 36. y sec x 1<br />
<br />
4<br />
x<br />
3 cot<br />
2<br />
37. y 1 38. y 2 cot x <br />
4 csc x <br />
In Exercises 39–48, use a graphing utility to graph the<br />
function. Include two full periods.<br />
<br />
2<br />
9. y sec 2x<br />
10.<br />
11. y 1 2 cot x<br />
12.<br />
13. y 1 14.<br />
2 sec x<br />
2<br />
y tan x 2<br />
y csc x<br />
y 2 sec<br />
x<br />
2<br />
39. y tan x 40. y tan 2x<br />
3<br />
41. y 2 sec 4x 42. y sec x<br />
<br />
4<br />
43. y tan x <br />
44. y 1 4 cot x <br />
45. y csc4x 46. y 2 sec2x <br />
47. 48. y 1 3 sec x<br />
y 0.1 tan <br />
x<br />
4 <br />
2 <br />
<br />
4<br />
<br />
2<br />
<br />
2
338 Chapter 4 Trigonometry<br />
In Exercises 49–56, use a graph to solve the equation on the<br />
interval [2, 2].<br />
49. tan x 1<br />
50. tan x 3<br />
51. cot x 3 52. cot x 1<br />
3<br />
53. sec x 2<br />
54. sec x 2<br />
55. csc x 2<br />
56.<br />
In Exercises 57–64, use the graph of the function to<br />
determine whether the function is even, odd, or neither.<br />
Verify your answer algebraically.<br />
65. GRAPHICAL REASONING Consider the functions<br />
given by<br />
and<br />
on the interval 0, .<br />
(a) Graph f and g in the same coordinate plane.<br />
(b) Approximate the interval in which f > g.<br />
(c) Describe the behavior of each of the functions as x<br />
approaches . How is the behavior of g related to<br />
the behavior of f as x approaches ?<br />
66. GRAPHICAL REASONING Consider the functions<br />
given by<br />
and<br />
on the interval 1, 1.<br />
(a) Use a graphing utility to graph f and g in the same<br />
viewing window.<br />
(b) Approximate the interval in which f < g.<br />
(c) Approximate the interval in which 2f < 2g. How<br />
does the result compare with that of part (b)?<br />
Explain.<br />
In Exercises 67–72, use a graphing utility to graph the two<br />
equations in the same viewing window. Use the graphs to<br />
determine whether the expressions are equivalent. Verify the<br />
results algebraically.<br />
67.<br />
68.<br />
69.<br />
gx<br />
f x 2 sin x<br />
f x tan<br />
y 1 cos x<br />
sin x ,<br />
x<br />
2<br />
y 1 sin x csc x,<br />
y 1 sin x sec x,<br />
y 2 cot x<br />
gx 1 2 csc x<br />
gx 1 2 sec<br />
y 2 1<br />
y 2 tan x<br />
csc x 23<br />
3<br />
57. f x sec x<br />
58. f x tan x<br />
59. gx cot x<br />
60. gx csc x<br />
61. f x x tan x 62. f x x 2 sec x<br />
63. gx x csc x 64. x 2 cot x<br />
x<br />
2<br />
70.<br />
71.<br />
72.<br />
In Exercises 73–76, match the function with its graph.<br />
Describe the behavior of the function as x approaches zero.<br />
[The graphs are labeled (a), (b), (c), and (d).]<br />
(a)<br />
(c)<br />
(b)<br />
(d)<br />
73. 74.<br />
75. 76.<br />
CONJECTURE In Exercises 77– 80, graph the functions f<br />
and g. Use the graphs to make a conjecture about the<br />
relationship between the functions.<br />
77.<br />
78.<br />
79.<br />
80.<br />
y 1 tan x cot 2 x,<br />
y 1 1 cot 2 x,<br />
y 1 sec 2 x 1,<br />
2<br />
−1<br />
−2<br />
−3<br />
−4<br />
−5<br />
−6<br />
4<br />
2<br />
−π<br />
−2<br />
−4<br />
f x x cos x <br />
gx x sin x<br />
y<br />
y<br />
π<br />
2<br />
f x sin x cos x gx 0<br />
2 ,<br />
2 ,<br />
f x sin x cos x <br />
π<br />
y 2 cot x<br />
y 2 csc 2 x<br />
y 2 tan 2 x<br />
x<br />
x<br />
gx 2 sin x<br />
f x sin 2 x, gx 1 21 cos 2x<br />
x<br />
f x cos gx 1 2 2 1 cos x<br />
2 ,<br />
In Exercises 81–84, use a graphing utility to graph the<br />
function and the damping factor of the function in the same<br />
viewing window. Describe the behavior of the function as x<br />
increases without bound.<br />
81. gx e x2 2<br />
sin x 82. f x e x cos x<br />
83. f x 2 x4 cos x 84. hx 2 x2 4<br />
sin x<br />
<br />
<br />
4<br />
3<br />
2<br />
1<br />
−π −1<br />
f x x sin x<br />
gx x cos x<br />
In Exercises 85–90, use a graphing utility to graph the<br />
function. Describe the behavior of the function as<br />
approaches zero.<br />
x<br />
85. y 6 cos x, x > 0 86. y 4 sin 2x, x > 0<br />
x x<br />
4<br />
2<br />
−4<br />
−2<br />
y<br />
y<br />
π 3π<br />
2 2<br />
π<br />
x<br />
x
Section 4.6 Graphs of Other Trigonometric Functions 339<br />
87. gx sin x<br />
88.<br />
x<br />
91. DISTANCE A plane flying at an altitude of 7 miles<br />
above a radar antenna will pass directly over the radar<br />
antenna (see figure). Let d be the ground distance from<br />
the antenna to the point directly under the plane and<br />
let x be the angle of elevation to the plane from the<br />
antenna. ( d is positive as the plane approaches the<br />
antenna.) Write d as a function of x and graph the<br />
function over the interval 0 < x < .<br />
x<br />
d<br />
f x 1 cos x<br />
x<br />
89. f x sin 1 90. hx x sin 1 x<br />
x<br />
Not drawn to scale<br />
7 mi<br />
92. TELEVISION COVERAGE A television camera is on a<br />
reviewing platform 27 meters from the street on which a<br />
parade will be passing from left to right (see figure).<br />
Write the distance d from the camera to a particular unit<br />
in the parade as a function of the angle x, and graph the<br />
function over the interval 2 < x < 2. (Consider<br />
x as negative when a unit in the parade approaches from<br />
the left.)<br />
Temperature<br />
(in degrees Fahrenheit)<br />
80<br />
60<br />
40<br />
20<br />
H(t)<br />
L(t)<br />
1 2 3 4 5 6 7 8 9 10 11 12<br />
Month of year<br />
(a) What is the period of each function?<br />
(b) During what part of the year is the difference<br />
between the normal high and normal low<br />
temperatures greatest? When is it smallest?<br />
(c) The sun is northernmost in the sky around June 21,<br />
but the graph shows the warmest temperatures at a<br />
later date. Approximate the lag time of the<br />
temperatures relative to the position of the sun.<br />
94. SALES The projected monthly sales S (in thousands of<br />
units) of lawn mowers (a seasonal product) are modeled<br />
by S 74 3t 40 cost6, where t is the time (in<br />
months), with t 1 corresponding to January. Graph<br />
the sales function over 1 year.<br />
95. HARMONIC MOTION An object weighing W pounds<br />
is suspended from the ceiling by a steel spring (see<br />
figure). The weight is pulled downward (positive<br />
direction) from its equilibrium position and released.<br />
The resulting motion of the weight is described by the<br />
function y 1 2 et4 cos 4t, t > 0, where y is the distance<br />
(in feet) and t is the time (in seconds).<br />
t<br />
Not drawn to scale<br />
27 m<br />
x<br />
d<br />
Equilibrium<br />
y<br />
Camera<br />
93. METEOROLOGY The normal monthly high temperatures<br />
H (in degrees Fahrenheit) in Erie, Pennsylvania<br />
are approximated by<br />
Ht 56.94 20.86 cost6 11.58 sint6<br />
and the normal monthly low temperatures L are<br />
approximated by<br />
Lt 41.80 17.13 cost6 13.39 sint6<br />
where t is the time (in months), with t 1 corresponding<br />
to January (see figure). (Source: National Climatic<br />
Data Center)<br />
(a) Use a graphing utility to graph the function.<br />
(b) Describe the behavior of the displacement function<br />
for increasing values of time t.<br />
EXPLORATION<br />
TRUE OR FALSE? In Exercises 96 and 97, determine<br />
whether the statement is true or false. Justify your answer.<br />
96. The graph of y csc x can be obtained on a calculator<br />
by graphing the reciprocal of y sin x.<br />
97. The graph of y sec x can be obtained on a<br />
calculator by graphing a translation of the reciprocal of<br />
y sin x.
340 Chapter 4 Trigonometry<br />
98. CAPSTONE Determine which function is represented<br />
by the graph. Do not use a calculator. Explain<br />
your reasoning.<br />
In Exercises 99 and 100, use a graphing utility to graph the<br />
function. Use the graph to determine the behavior of the<br />
function as x → c.<br />
(a)<br />
(b)<br />
(a)<br />
(i)<br />
(ii)<br />
π<br />
−<br />
4<br />
3<br />
2<br />
1<br />
y<br />
π<br />
4<br />
π<br />
2<br />
f x tan 2x<br />
f x tanx2<br />
<br />
x →<br />
2 as x approaches<br />
<br />
x →<br />
2 as x approaches<br />
<br />
(c) x → <br />
2 as x approaches <br />
2 from the right <br />
<br />
(d) x → <br />
2 as x approaches <br />
2 from the left <br />
99. f x tan x 100. f x sec x<br />
In Exercises 101 and 102, use a graphing utility to graph the<br />
function. Use the graph to determine the behavior of the<br />
function as x → c.<br />
(a) As x → 0 , the value of f x →.<br />
(b) As x → 0 , the value of f x →.<br />
(c) As x → <br />
, the value of f x →.<br />
(d) As x → <br />
, the value of f x →.<br />
101. f x cot x 102. f x csc x<br />
x<br />
<br />
2 from the right <br />
103. THINK ABOUT IT Consider the function given by<br />
f x x cos x.<br />
<br />
(b)<br />
π<br />
−<br />
2<br />
2 from the left <br />
(a) Use a graphing utility to graph the function and<br />
verify that there exists a zero between 0 and 1. Use<br />
the graph to approximate the zero.<br />
(i)<br />
(ii)<br />
<br />
π<br />
−<br />
4<br />
(iii) f x 2 tan x (iii) f x cscx4<br />
(iv) f x tan 2x (iv) f x secx4<br />
(v) f x tanx2 (v) f x csc4x <br />
<br />
y<br />
π<br />
4<br />
π<br />
2<br />
f x sec 4x<br />
f x csc 4x<br />
x<br />
(b) Starting with x 0 1, generate a sequence x 1 , x 2 ,<br />
x 3 , . . . , where x n cosx n1 . For example,<br />
x 0 1<br />
x 1 cosx 0 <br />
x 2 cosx 1 <br />
x 3 cosx 2 <br />
<br />
What value does the sequence approach?<br />
104. AP<strong>PRO</strong>XIMATION Using calculus, it can be shown<br />
that the tangent function can be approximated by the<br />
polynomial<br />
tan x x 2x3<br />
3! 16x 5<br />
5!<br />
where x is in radians. Use a graphing utility to graph<br />
the tangent function and its polynomial approximation<br />
in the same viewing window. How do the graphs<br />
compare?<br />
105. AP<strong>PRO</strong>XIMATION Using calculus, it can be shown<br />
that the secant function can be approximated by the<br />
polynomial<br />
sec x 1 x 2<br />
2! 5x4<br />
4!<br />
where x is in radians. Use a graphing utility to graph<br />
the secant function and its polynomial approximation<br />
in the same viewing window. How do the graphs<br />
compare?<br />
106. PATTERN RECOGNITION<br />
(a) Use a graphing utility to graph each function.<br />
y 1 4<br />
sin x 1 3 sin 3x <br />
y 2 4<br />
sin x 1 3 sin 3x 1 5 sin 5x <br />
(b) Identify the pattern started in part (a) and find a<br />
function y 3 that continues the pattern one more<br />
term. Use a graphing utility to graph y 3 .<br />
(c) The graphs in parts (a) and (b) approximate the<br />
periodic function in the figure. Find a function y 4<br />
that is a better approximation.<br />
1<br />
y<br />
3<br />
x
Section 4.7 Inverse Trigonometric Functions 341<br />
4.7 INVERSE TRIGONOMETRIC FUNCTIONS<br />
NASA<br />
What you should learn<br />
• Evaluate and graph the inverse<br />
sine function.<br />
• Evaluate and graph the other<br />
inverse trigonometric functions.<br />
• Evaluate and graph the<br />
compositions of trigonometric<br />
functions.<br />
Why you should learn it<br />
You can use inverse trigonometric<br />
functions to model and solve<br />
real-life problems. For instance,<br />
in Exercise 106 on page 349, an<br />
inverse trigonometric function can be<br />
used to model the angle of elevation<br />
from a television camera to a space<br />
shuttle launch.<br />
When evaluating the inverse sine<br />
function, it helps to remember<br />
the phrase “the arcsine of x is<br />
the angle (or number) whose<br />
sine is x.”<br />
Inverse Sine Function<br />
Recall from Section 1.9 that, for a function to have an inverse function, it must be<br />
one-to-one—that is, it must pass the Horizontal Line Test. From Figure 4.71, you can<br />
see that y sin x does not pass the test because different values of x yield the same<br />
y-value.<br />
FIGURE 4.71<br />
However, if you restrict the domain to the interval 2 x 2<br />
(corresponding to the black portion of the graph in Figure 4.71), the following properties<br />
hold.<br />
1. On the interval 2, 2, the function y sin x is increasing.<br />
2. On the interval 2, 2, y sin x takes on its full range of values,<br />
1 sin x 1.<br />
3. On the interval 2, 2, y sin x is one-to-one.<br />
So, on the restricted domain 2 x 2, y sin x has a unique inverse<br />
function called the inverse sine function. It is denoted by<br />
y arcsin x<br />
or<br />
−π<br />
1<br />
−1<br />
sin x has an inverse function<br />
on <strong>this</strong> interval.<br />
y sin 1 x.<br />
y<br />
y = sin x<br />
The notation sin 1 x is consistent with the inverse function notation f 1 x. The arcsin x<br />
notation (read as “the arcsine of x”) comes from the association of a central angle with<br />
its intercepted arc length on a unit circle. So, arcsin x means the angle (or arc) whose<br />
sine is x. Both notations, arcsin x and sin 1 x, are commonly used in mathematics, so<br />
remember that sin 1 x denotes the inverse sine function rather than 1sin x. The values<br />
of arcsin x lie in the interval 2 arcsin x 2. The graph of y arcsin x is<br />
shown in Example 2.<br />
Definition of Inverse Sine Function<br />
The inverse sine function is defined by<br />
y arcsin x<br />
if and only if<br />
where 1 x 1 and 2 y 2. The domain of y arcsin x is<br />
1, 1, and the range is 2, 2.<br />
π<br />
sin y x<br />
x
342 Chapter 4 Trigonometry<br />
Example 1<br />
Evaluating the Inverse Sine Function<br />
As with the trigonometric<br />
functions, much of the work<br />
with the inverse trigonometric<br />
functions can be done by exact<br />
calculations rather than by<br />
calculator approximations.<br />
Exact calculations help to<br />
increase your understanding of<br />
the inverse functions by relating<br />
them to the right triangle<br />
definitions of the trigonometric<br />
functions.<br />
If possible, find the exact value.<br />
a. b. sin c. sin 1 2<br />
2<br />
arcsin 1 2<br />
Solution<br />
a. Because sin for <br />
it follows that<br />
6 1 2 2 y 2 ,<br />
arcsin 1 Angle whose sine is 1 2<br />
2 6 .<br />
<br />
<br />
b. Because sin for <br />
it follows that<br />
3 3<br />
2 2 y 2 ,<br />
sin 13<br />
Angle whose sine is 32<br />
2 3 .<br />
<br />
<br />
1<br />
3<br />
<br />
c. It is not possible to evaluate y sin 1 x when x 2 because there is no angle whose<br />
sine is 2. Remember that the domain of the inverse sine function is 1, 1.<br />
Now try Exercise 5.<br />
<br />
<br />
<br />
Example 2<br />
Graphing the Arcsine Function<br />
( )<br />
2<br />
,<br />
2<br />
( )<br />
−<br />
1<br />
, −<br />
π<br />
2 6<br />
( )<br />
−1, −<br />
π<br />
2<br />
FIGURE 4.72<br />
π<br />
4<br />
π<br />
2<br />
(0, 0)<br />
y<br />
( 1, )<br />
( )<br />
1<br />
,<br />
2<br />
π<br />
2<br />
π<br />
6<br />
1<br />
y = arcsin x<br />
2<br />
( − , −<br />
π<br />
π 2 4 )<br />
−<br />
2<br />
x<br />
Sketch a graph of<br />
y arcsin x.<br />
Solution<br />
By definition, the equations y arcsin x and sin y x are equivalent for<br />
2 y 2. So, their graphs are the same. From the interval 2, 2, you<br />
can assign values to y in the second equation to make a table of values. Then plot the<br />
points and draw a smooth curve through the points.<br />
y<br />
<br />
<br />
2<br />
The resulting graph for y arcsin x is shown in Figure 4.72. Note that it is the<br />
reflection (in the line y x) of the black portion of the graph in Figure 4.71. Be sure<br />
you see that Figure 4.72 shows the entire graph of the inverse sine function. Remember<br />
that the domain of y arcsin x is the closed interval 1, 1 and the range is the closed<br />
interval 2, 2.<br />
Now try Exercise 21.<br />
<br />
<br />
4<br />
x sin y 1 2<br />
2<br />
<br />
<br />
6<br />
1 2<br />
0<br />
0<br />
<br />
6<br />
1<br />
2<br />
<br />
4<br />
2<br />
2<br />
<br />
2<br />
1
Section 4.7 Inverse Trigonometric Functions 343<br />
Other Inverse Trigonometric Functions<br />
The cosine function is decreasing and one-to-one on the interval 0 x , as shown<br />
in Figure 4.73.<br />
y<br />
y = cos x<br />
−π<br />
π π 2π<br />
−1 2<br />
x<br />
cos x has an inverse function<br />
on <strong>this</strong> interval.<br />
FIGURE 4.73<br />
Consequently, on <strong>this</strong> interval the cosine function has an inverse function—the inverse<br />
cosine function—denoted by<br />
y arccos x<br />
or<br />
y cos 1 x.<br />
Similarly, you can define an inverse tangent function by restricting the domain of<br />
y tan x to the interval 2, 2. The following list summarizes the definitions of<br />
the three most common inverse trigonometric functions. The remaining three are<br />
defined in Exercises 115–117.<br />
Definitions of the Inverse Trigonometric Functions<br />
Function Domain Range<br />
y arcsin x if and only if sin y x 1 x 1<br />
y arccos x if and only if cos y x 1 x 1 0 y <br />
y arctan x if and only if tan y x < x < <br />
<br />
<br />
<br />
<br />
<br />
2 y 2<br />
<br />
<br />
2 < y < 2<br />
The graphs of these three inverse trigonometric functions are shown in Figure 4.74.<br />
y<br />
y<br />
y<br />
π<br />
2<br />
π<br />
π<br />
2<br />
−1<br />
y = arcsin x<br />
x<br />
1<br />
π<br />
2<br />
y = arccos x<br />
−2<br />
−1<br />
y = arctan x<br />
x<br />
1 2<br />
π<br />
−<br />
2<br />
−1<br />
1<br />
x<br />
π<br />
−<br />
2<br />
DOMAIN:<br />
RANGE: <br />
FIGURE 4.74<br />
1, 1<br />
2,<br />
2<br />
<br />
DOMAIN: 1, 1<br />
RANGE: 0, <br />
DOMAIN:<br />
RANGE: <br />
, <br />
2,<br />
2
344 Chapter 4 Trigonometry<br />
Example 3<br />
Evaluating Inverse Trigonometric Functions<br />
Find the exact value.<br />
a. arccos 2 b.<br />
2<br />
c. arctan 0<br />
d.<br />
cos 1 1<br />
tan 1 1<br />
Solution<br />
a. Because cos4 22, and 4 lies in 0, , it follows that<br />
arccos 2<br />
Angle whose cosine is 22<br />
2 4 .<br />
b. Because cos 1, and lies in 0, , it follows that<br />
cos 1 1 .<br />
Angle whose cosine is 1<br />
c. Because tan 0 0, and 0 lies in 2, 2, it follows that<br />
arctan 0 0.<br />
<br />
Angle whose tangent is 0<br />
d. Because tan4 1, and 4 lies in 2, 2, it follows that<br />
tan 1 1 <br />
Angle whose tangent is 1<br />
4 .<br />
<br />
<br />
Now try Exercise 15.<br />
Example 4<br />
Calculators and Inverse Trigonometric Functions<br />
Use a calculator to approximate the value (if possible).<br />
a. arctan8.45<br />
b. sin 1 0.2447<br />
c. arccos 2<br />
WARNING / CAUTION<br />
Remember that the domain of the<br />
inverse sine function and the<br />
inverse cosine function is 1, 1,<br />
as indicated in Example 4(c).<br />
Solution<br />
Function Mode Calculator Keystrokes<br />
a. arctan8.45 Radian 8.45<br />
From the display, it follows that arctan8.45 1.453001.<br />
b. sin 1 0.2447 Radian SIN 1 0.2447<br />
From the display, it follows that sin 1 0.2447 0.2472103.<br />
c. arccos 2<br />
Radian COS 1 2<br />
TAN 1 ENTER<br />
ENTER<br />
ENTER<br />
In real number mode, the calculator should display an error message because the<br />
domain of the inverse cosine function is 1, 1.<br />
Now try Exercise 29.<br />
In Example 4, if you had set the calculator to degree mode, the displays would have<br />
been in degrees rather than radians. This convention is peculiar to calculators. By<br />
definition, the values of inverse trigonometric functions are always in radians.
Section 4.7 Inverse Trigonometric Functions 345<br />
You can review the composition<br />
of functions in Section 1.8.<br />
Compositions of Functions<br />
Recall from Section 1.9 that for all x in the domains of f and f 1 , inverse functions have<br />
the properties<br />
f f 1 x x and f 1 f x x.<br />
Inverse Properties of Trigonometric Functions<br />
If 1 x 1 and 2 y 2, then<br />
sinarcsin x x and arcsinsin y y.<br />
If 1 x 1 and 0 y , then<br />
cosarccos x x and arccoscos y y.<br />
If x is a real number and 2 < y < 2, then<br />
tanarctan x x and arctantan y y.<br />
Keep in mind that these inverse properties do not apply for arbitrary values of x and<br />
y. For instance,<br />
arcsin sin 3<br />
2 arcsin1 2 3<br />
2 .<br />
In other words, the property<br />
arcsinsin y y<br />
is not valid for values of y outside the interval 2, 2.<br />
<br />
Example 5<br />
Using Inverse Properties<br />
If possible, find the exact value.<br />
a. tanarctan5 b. arcsin sin 5 c.<br />
3<br />
<br />
coscos 1 <br />
Solution<br />
a. Because 5 lies in the domain of the arctan function, the inverse property applies,<br />
and you have<br />
tanarctan5 5.<br />
b. In <strong>this</strong> case, 53 does not lie within the range of the arcsine function,<br />
2 y 2. However, 53 is coterminal with<br />
5<br />
3 2 <br />
3<br />
which does lie in the range of the arcsine function, and you have<br />
arcsin sin 5<br />
<br />
<br />
3<br />
arcsin sin 3 <br />
c. The expression coscos 1 is not defined because cos 1 is not defined.<br />
Remember that the domain of the inverse cosine function is 1, 1.<br />
Now try Exercise 49.<br />
<br />
3 .
346 Chapter 4 Trigonometry<br />
y<br />
Example 6 shows how to use right triangles to find exact values of<br />
compositions of inverse functions. Then, Example 7 shows how to use right triangles to<br />
convert a trigonometric expression into an algebraic expression. This conversion<br />
technique is used frequently in calculus.<br />
3 2 2<br />
3 − 2 = 5<br />
u = arccos<br />
2<br />
2<br />
3<br />
2<br />
Angle whose cosine is 3<br />
FIGURE 4.75<br />
y<br />
5 2 − (−3) 2 = 4<br />
u = arcsin − 3 5<br />
5<br />
Angle whose sine is 3 5<br />
FIGURE 4.76<br />
(<br />
(<br />
−3<br />
x<br />
x<br />
Example 6<br />
Find the exact value.<br />
tan arccos 2 3<br />
a. b.<br />
Solution<br />
Evaluating Compositions of Functions<br />
a. If you let u arccos 2 then cos u 2 3 ,<br />
3 . Because cos u is positive, u is a first-quadrant<br />
angle. You can sketch and label angle u as shown in Figure 4.75. Consequently,<br />
tan arccos 2 3<br />
b. If you let u arcsin3 5, then sin u 3 5 . Because sin u is negative, u is a fourthquadrant<br />
angle. You can sketch and label angle u as shown in Figure 4.76.<br />
Consequently,<br />
cos arcsin 3 5<br />
cos arcsin 3 5<br />
tan u <br />
opp<br />
adj 5<br />
2 .<br />
Now try Exercise 57.<br />
cos u <br />
adj<br />
hyp 4 5 .<br />
Example 7<br />
Some Problems from Calculus<br />
Write each of the following as an algebraic expression in x.<br />
a. sinarccos 3x, 0 x 1 b.<br />
3<br />
cotarccos 3x,<br />
0 x < 1 3<br />
1<br />
u = arccos 3x<br />
3x<br />
Angle whose cosine is 3x<br />
FIGURE 4.77<br />
1 − (3x) 2<br />
Solution<br />
If you let u arccos 3x, then cos u 3x, where 1 3x 1. Because<br />
you can sketch a right triangle with acute angle u, as shown in Figure 4.77. From <strong>this</strong><br />
triangle, you can easily convert each expression to algebraic form.<br />
a.<br />
b.<br />
cos u adj<br />
hyp 3x<br />
1<br />
sinarccos 3x sin u opp<br />
hyp 1 9x 2 ,<br />
cotarccos 3x cot u adj<br />
opp <br />
Now try Exercise 67.<br />
0 x 1 3<br />
3x<br />
0 x < 1 1 9x 2, 3<br />
In Example 7, similar arguments can be made for x-values lying in the interval<br />
1 3, 0.
Section 4.7 Inverse Trigonometric Functions 347<br />
4.7 EXERCISES<br />
VOCABULARY: Fill in the blanks.<br />
Function Alternative Notation Domain Range<br />
1. y arcsin x __________ __________<br />
2. __________ y cos 1 x 1 x 1 __________<br />
3. y arctan x __________ __________ __________<br />
4. Without restrictions, no trigonometric function has a(n) __________ function.<br />
SKILLS AND APPLICATIONS<br />
See www.CalcChat.com for worked-out solutions to odd-numbered exercises.<br />
<br />
<br />
<br />
2 y 2<br />
In Exercises 5–20, evaluate the expression without using a<br />
calculator.<br />
5. arcsin 1 2<br />
6. arcsin 0<br />
7. arccos 1 2<br />
8. arccos 0<br />
9. arctan 3<br />
3<br />
10. arctan1<br />
11. cos<br />
1 3 2 <br />
12.<br />
13. arctan3 14.<br />
15. 16.<br />
17. sin<br />
1 3<br />
18.<br />
2 <br />
In Exercises 21 and 22, use a graphing utility to graph f, g, and<br />
y x in the same viewing window to verify geometrically that<br />
g is the inverse function of f. (Be sure to restrict the domain<br />
of f properly.)<br />
21.<br />
22.<br />
arccos 1 2<br />
f x sin x,<br />
f x tan x,<br />
gx arcsin x<br />
gx arctan x<br />
sin 1 2 2 <br />
arctan3<br />
arcsin 2<br />
2<br />
tan 1 3 3 <br />
19. tan 1 0<br />
20. cos 1 1<br />
In Exercises 23–40, use a calculator to evaluate the<br />
expression. Round your result to two decimal places.<br />
23. arccos 0.37 24. arcsin 0.65<br />
25. arcsin0.75 26. arccos0.7<br />
27. arctan3<br />
28. arctan 25<br />
29. sin 1 0.31<br />
30. cos 1 0.26<br />
31. arccos0.41 32. arcsin0.125<br />
33. arctan 0.92<br />
34. arctan 2.8<br />
35. arcsin 7 36. arccos 1 8<br />
3<br />
37. tan1 19<br />
38. tan 1 95<br />
4<br />
7 <br />
39. tan 1 372 40. tan 1 2165<br />
In Exercises 41 and 42, determine the missing coordinates of<br />
the points on the graph of the function.<br />
41. 42.<br />
y = arctan x<br />
−3 −2<br />
In Exercises 43– 48, use an inverse trigonometric function to<br />
write as a function of x.<br />
<br />
43. 44.<br />
θ<br />
45. 46.<br />
θ<br />
5<br />
4<br />
π<br />
π 2 4<br />
( − 3, )<br />
47. 48.<br />
2x<br />
y<br />
θ<br />
x + 3<br />
( )<br />
π<br />
, 4<br />
1 2 3<br />
π<br />
, − 6<br />
( )<br />
x<br />
x + 2<br />
π<br />
(−1, )<br />
1<br />
( −<br />
2 , ) π<br />
( , )<br />
θ<br />
x 2 − 1<br />
In Exercises 49–54, use the properties of inverse trigonometric<br />
functions to evaluate the expression.<br />
49. sinarcsin 0.3 50. tanarctan 45<br />
51. cosarccos0.1 52. sinarcsin0.2<br />
53. arcsinsin 3 54. arccos cos 7<br />
2<br />
<br />
x<br />
−2<br />
θ<br />
θ<br />
−1<br />
x<br />
π<br />
4<br />
4<br />
10<br />
y<br />
y = arccos x<br />
6<br />
1 2<br />
x + 1<br />
x − 1<br />
x
348 Chapter 4 Trigonometry<br />
In Exercises 55–66, find the exact value of the expression.<br />
(Hint: Sketch a right triangle.)<br />
55. sinarctan 3 4<br />
56. secarcsin 4 5<br />
57. costan 1 2<br />
58. sin cos 15<br />
5 <br />
59. cosarcsin 13<br />
5 60. cscarctan12<br />
5<br />
61. secarctan 3 5 62. tanarcsin 3 4<br />
63. sinarccos 2 3 64. cotarctan 5 8<br />
65. 66.<br />
In Exercises 67–76, write an algebraic expression that is<br />
equivalent to the expression. (Hint: Sketch a right triangle, as<br />
demonstrated in Example 7.)<br />
67.<br />
68.<br />
69.<br />
70.<br />
71.<br />
72.<br />
73.<br />
74.<br />
75.<br />
76.<br />
In Exercises 77 and 78, use a graphing utility to graph f<br />
and g in the same viewing window to verify that the two<br />
functions are equal. Explain why they are equal. Identify any<br />
asymptotes of the graphs.<br />
77.<br />
78.<br />
In Exercises 79–82, fill in the blank.<br />
79.<br />
80.<br />
81.<br />
csc cos 3 1 2 <br />
cotarctan x<br />
sinarctan x<br />
cosarcsin 2x<br />
secarctan 3x<br />
sinarccos x<br />
secarcsinx 1<br />
tan arccos<br />
3<br />
x<br />
cot arctan 1 x<br />
csc arctan<br />
arccos<br />
2<br />
x<br />
cos arcsin x h<br />
r<br />
arctan 9 x arcsin ,<br />
arcsin 36 x 2<br />
6<br />
<br />
fx sinarctan 2x,<br />
f x tan arccos x 2 ,<br />
gx <br />
arccos,<br />
sec sin 1 2 2 <br />
x 0<br />
2x<br />
1 4x 2<br />
gx 4 x 2<br />
x<br />
3<br />
x 2 2x 10 arcsin <br />
0 x 6<br />
82.<br />
In Exercises 83 and 84, sketch a graph of the function and<br />
compare the graph of g with the graph of f x arcsin x.<br />
83.<br />
84.<br />
In Exercises 85–90, sketch a graph of the function.<br />
85.<br />
86.<br />
87.<br />
88.<br />
89.<br />
90.<br />
In Exercises 91–96, use a graphing utility to graph the<br />
function.<br />
91.<br />
92.<br />
93.<br />
94.<br />
95.<br />
96.<br />
In Exercises 97 and 98, write the function in terms of the sine<br />
function by using the identity<br />
A cos t 1 B sin t A 2 1 B 2 sin t 1 arctan A B .<br />
Use a graphing utility to graph both forms of the function.<br />
What does the graph imply?<br />
97.<br />
98.<br />
arccos x 2<br />
2<br />
gx arcsinx 1<br />
gx arcsin x 2<br />
y 2 arccos x<br />
gt arccost 2<br />
f x) arctan 2x<br />
<br />
f x <br />
2 arctan x<br />
hv tanarccos v<br />
f x arccos x 4<br />
f x 2 arccos2x<br />
f x arcsin4x<br />
f x arctan2x 3<br />
f x 3 arctanx<br />
f x sin 2 3<br />
1<br />
<br />
<br />
f x <br />
2 1 cos1<br />
arctan,<br />
f t 3 cos 2t 3 sin 2t<br />
f t 4 cos t 3 sin t<br />
x 2 2<br />
In Exercises 99–104, fill in the blank. If not possible,<br />
state the reason. (Note: The notation x → c indicates that<br />
x approaches c from the right and x → c indicates that x<br />
approaches c from the left.)<br />
99. As x → 1 , the value of arcsin x →.<br />
100. As x → 1 , the value of arccos x →.
Section 4.7 Inverse Trigonometric Functions 349<br />
101. As x →, the value of arctan x →.<br />
102. As x → 1 , the value of arcsin x →.<br />
103. As x → 1 , the value of arccos x →.<br />
104. As x → , the value of arctan x →.<br />
105. DOCKING A BOAT A boat is pulled in by means of<br />
a winch located on a dock 5 feet above the deck of the<br />
boat (see figure). Let be the angle of elevation from<br />
the boat to the winch and let s be the length of the rope<br />
from the winch to the boat.<br />
5 ft<br />
(a) Write<br />
as a function of s.<br />
(b) Find when s 40 feet and s 20 feet.<br />
106. PHOTOGRAPHY A television camera at ground<br />
level is filming the lift-off of a space shuttle at a point<br />
750 meters from the launch pad (see figure). Let be<br />
the angle of elevation to the shuttle and let s be the<br />
height of the shuttle.<br />
(a) Write<br />
<br />
<br />
θ<br />
<br />
<br />
as a function of s.<br />
107. PHOTOGRAPHY A photographer is taking a picture<br />
of a three-foot-tall painting hung in an art gallery.<br />
The camera lens is 1 foot below the lower edge of the<br />
painting (see figure). The angle subtended by the<br />
camera lens x feet from the painting is<br />
arctan<br />
3x<br />
x 2 4 ,<br />
<br />
s<br />
θ<br />
750 m<br />
(b) Find when s 300 meters and s 1200<br />
meters.<br />
x > 0.<br />
<br />
<br />
s<br />
Not drawn to scale<br />
3 ft<br />
1 ft<br />
(a) Use a graphing utility to graph<br />
as a function of x.<br />
(b) Move the cursor along the graph to approximate<br />
the distance from the picture when is maximum.<br />
(c) Identify the asymptote of the graph and discuss its<br />
meaning in the context of the problem.<br />
108. GRANULAR ANGLE OF REPOSE Different types of<br />
granular substances naturally settle at different angles<br />
when stored in cone-shaped piles. This angle is<br />
called the angle of repose (see figure). When rock<br />
salt is stored in a cone-shaped pile 11 feet high, the<br />
diameter of the pile’s base is about 34 feet. (Source:<br />
Bulk-Store Structures, Inc.)<br />
(a) Find the angle of repose for rock salt.<br />
(b) How tall is a pile of rock salt that has a base<br />
diameter of 40 feet?<br />
109. GRANULAR ANGLE OF REPOSE When whole<br />
corn is stored in a cone-shaped pile 20 feet high, the<br />
diameter of the pile’s base is about 82 feet.<br />
(a) Find the angle of repose for whole corn.<br />
(b) How tall is a pile of corn that has a base diameter<br />
of 100 feet?<br />
110. ANGLE OF ELEVATION An airplane flies at an<br />
altitude of 6 miles toward a point directly over an<br />
observer. Consider and x as shown in the figure.<br />
θ<br />
θ<br />
17 ft<br />
<br />
x<br />
α<br />
x<br />
β<br />
11 ft<br />
θ<br />
Not drawn to scale<br />
<br />
<br />
6 mi<br />
<br />
Not drawn to scale<br />
(a) Write<br />
<br />
<br />
as a function of x.<br />
(b) Find when x 7 miles and x 1 mile.
350 Chapter 4 Trigonometry<br />
111. SECURITY PATROL A security car with its spotlight<br />
on is parked 20 meters from a warehouse. Consider<br />
and as shown in the figure.<br />
(a) Write<br />
as a function of x.<br />
(b) Find when x 5 meters and x 12 meters.<br />
EXPLORATION<br />
TRUE OR FALSE? In Exercises 112–114, determine<br />
whether the statement is true or false. Justify your answer.<br />
112.<br />
113.<br />
114.<br />
<br />
<br />
arctan x arcsin x<br />
arccos x<br />
115. Define the inverse cotangent function by restricting the<br />
domain of the cotangent function to the interval 0, ,<br />
and sketch its graph.<br />
116. Define the inverse secant function by restricting the<br />
domain of the secant function to the intervals 0, 2<br />
and 2, , and sketch its graph.<br />
117. Define the inverse cosecant function by restricting the<br />
domain of the cosecant function to the intervals<br />
2, 0 and 0, 2, and sketch its graph.<br />
In Exercises 119–126, use the results of Exercises 115–117 to<br />
evaluate each expression without using a calculator.<br />
119. arcsec2<br />
120. arcsec 1<br />
121. arccot1<br />
122. arccot3<br />
123. arccsc 2<br />
124. arccsc1<br />
125. arccsc <br />
23<br />
126. arcsec 23<br />
3 <br />
3 <br />
x<br />
sin 5<br />
arcsin 1 2 5<br />
6 1 2<br />
6<br />
tan 5<br />
arctan 1 5<br />
4 1 4<br />
In Exercises 127–134, use the results of Exercises 115–117<br />
and a calculator to approximate the value of the expression.<br />
Round your result to two decimal places.<br />
127. arcsec 2.54 128. arcsec1.52<br />
129. arccot 5.25 130. arccot10<br />
131. arccot 5 3<br />
132. arccot 16<br />
7 <br />
133. arccsc 25 3 134. arccsc12<br />
135. AREA In calculus, it is shown that the area of<br />
the region bounded by the graphs of y 0,<br />
y 1x 2 1, x a, and x b is given by<br />
Area arctan b arctan a<br />
(see figure). Find the area for the following values of a<br />
and b.<br />
(a)<br />
(c)<br />
(b)<br />
(d)<br />
136. THINK ABOUT IT Use a graphing utility to graph<br />
the functions<br />
f x x<br />
and<br />
For x > 0, it appears that g > f. Explain why you<br />
know that there exists a positive real number a such<br />
that g < f for x > a. Approximate the number a.<br />
137. THINK ABOUT IT Consider the functions given by<br />
f x sin x and f 1 x arcsin x.<br />
(a) Use a graphing utility to graph the composite<br />
functions f f 1 and f 1 f.<br />
(b) Explain why the graphs in part (a) are not the<br />
graph of the line y x. Why do the graphs of<br />
f f 1 and f 1 f differ?<br />
138. <strong>PRO</strong>OF Prove each identity.<br />
(a) arcsinx arcsin x<br />
(b) arctanx arctan x<br />
(c)<br />
a 0, b 1<br />
a 0, b 3<br />
−2 a b 2<br />
gx 6 arctan x.<br />
<br />
arctan x arctan 1 x 2 ,<br />
<br />
(d) arcsin x arccos x <br />
2<br />
x<br />
(e) arcsin x arctan<br />
1 x 2<br />
1<br />
y<br />
a 1, b 1<br />
a 1, b 3<br />
y =<br />
1<br />
x 2 + 1<br />
x<br />
x > 0
ERROR: rangecheck<br />
OFFENDING COMMAND: .buildshading2<br />
STACK:<br />
-dictionary-<br />
-dictionary-