Pre-Algebra Chapter 9

CLASSIFY ANGLES
Angles can be classified by their degree measure.
Study Tip
Common
Misconception
You may think that a right
angle must always face to
the right. However, a right
angle can be in any
position.
A
This symbol is
used to indicate
a right angle.
Types of Angles
Acute Angle Right Angle Obtuse Angle Straight Angle
A A A
0° mA 90° mA 90° 90° mA 180° mA 180°
Example 3
Classify Angles
Classify each angle as acute, obtuse, right, or straight.
a. A
b. c.
B
D
125˚
C
E
F
G
H
40˚
J
mABC 90. mDEF 90. mGHJ 90.
So, ABC is obtuse. So, DEF is right. So, GHJ is acute.
Example 4
Use Angles to Solve a Problem
RACING The diagram shows the angle of the
track at a corner of the Texas Motor Speedway
in Fort Worth, Texas. Classify this angle.
Since 24° is greater than 0° and less than 90°,
the angle is acute.
24˚
SNFR
Concept Check
1. Name the vertex and sides of the angle shown.
Then name the angle in four ways.
M
Guided Practice
Application
www.pre-alg.com/extra_examples
2. OPEN ENDED Draw an obtuse angle.
Use a protractor to find the measure
of each angle. Then classify each angle
as acute, obtuse, right, or straight.
3. CED 4. BED
5. CEB 6. AED
Use a protractor to draw an angle having each measurement. Then classify
each angle as acute, obtuse, right, or straight.
7. 55° 8. 140°
9. TIME What type of angle is formed by the hands on a clock at 6:00?
A
N
E
1
B
P
C
D
Lesson 9-3 Angles 449