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B<br />

C 12. In the diagram shown, ^ ABC is an isosceles triangle where .<br />

a. Draw the scalar projection of on .<br />

b. Relocate b ! a ! c !<br />

0a ! 0 @ b ! @<br />

a<br />

b<br />

u u A<br />

, and draw the scalar projection of on .<br />

c. Explain why the scalar projection of on is the same as the scalar<br />

projection of b ! on c !<br />

a ! c !<br />

b !<br />

c !<br />

c<br />

.<br />

d. Does the vector projection of on equal the vector projection of on ?<br />

13. Vectors and b !<br />

a ! c !<br />

are such that and @ b ! b !<br />

c !<br />

a ! 0a ! 0 10 @ 12, and the angle between<br />

them is 135° .<br />

a. Show that the scalar projection of on does not equal the scalar<br />

projection of b ! on a !<br />

a ! b !<br />

.<br />

b. Draw diagrams to illustrate the corresponding vector projections associated<br />

with part a.<br />

14. You are given the vector OD ! 11, 2, 22 and the three points, A12, 1, 42,<br />

B11, 3, 32, and C16, 7, 52.<br />

a. Calculate the scalar projection of AB !<br />

on OD !<br />

.<br />

b. Verify computationally that the scalar projection of on added<br />

to the scalar projection of on equals the scalar projection of<br />

AC ! on OD !<br />

BC ! OD !<br />

AB !<br />

OD !<br />

.<br />

c. Explain why this same result is also true for the corresponding vector<br />

projections.<br />

15. a. If , , and represent the direction angles for vector OP !<br />

T<br />

a b g<br />

, prove that<br />

cos 2 a cos 2 b cos 2 g 1.<br />

b. Determine the coordinates of a vector OP !<br />

that makes an angle of 30° with<br />

the y-axis, 60° with the z-axis, and 90° with the x-axis.<br />

c. In Example 3, it was shown that, in general, the direction angles do not<br />

always add to 180° —that is, a b g 180° . Under what conditions,<br />

however, must the direction angles always add to 180° ?<br />

PART C<br />

16. A vector in R 3 makes equal angles with the coordinate axes. Determine the<br />

size of each of these angles if the angles are<br />

a. acute b. obtuse<br />

17. If a, b, and g represent the direction angles for vector OP !<br />

, prove that<br />

sin 2 a sin 2 .<br />

18. Vectors OA !<br />

b sin 2<br />

and OB !<br />

g 2<br />

are not collinear. The sum of the direction angles of<br />

each vector is 180° . Draw diagrams to illustrate possible positions of points<br />

A and B.<br />

400 7.5 SCALAR AND VECTOR PROJECTIONS<br />

NEL

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