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Exercise 7.3<br />

C<br />

K<br />

PART A<br />

1. If a ! # b ! 0, why can we not necessarily conclude that the given vectors are<br />

perpendicular? (In other words, what restrictions must be placed on the<br />

vectors to make this statement true?)<br />

2. Explain why the calculation 1a ! !<br />

# b 2 #<br />

! c is not meaningful.<br />

3. A student writes the statement a ! !<br />

# ! and then concludes that a ! c ! b b #<br />

! c .<br />

Construct a simple numerical example to show that this is not correct if the<br />

given vectors are all nonzero.<br />

! !<br />

4. Why is it correct to say that if then<br />

5. If two vectors are unit vectors pointing in opposite directions, what is<br />

the value of a ! a ! ! and b ! a ! !<br />

# ! b b #<br />

! a c , c ?<br />

# b ?<br />

PART B<br />

6. If u is the angle (in degrees) between the two given vectors, calculate the dot<br />

product of the vectors.<br />

a. 0p ! d.<br />

b. 0x ! 0 4, 0q ! e.<br />

c. 0a ! 0 2, 0y ! 0 8, u 60°<br />

0p !<br />

0 0, @b ! 0m ! 0 1, 0q !<br />

f. 0u ! 0 2, 0n ! 0 1, u 180°<br />

0 4, u 150°<br />

0 4, 0v ! 0 5, u 90°<br />

@ 8, u 100°<br />

0 8, u 145°<br />

7. Calculate, to the nearest degree, the angle between the given vectors.<br />

! !<br />

a. d. 0p !<br />

! !<br />

b. e. 0a ! 0 1, 0q !<br />

! !<br />

c. f.<br />

8. For the two vectors a ! and b !<br />

0u ! 0 7, @b ! 0 5, p ! #<br />

! 0x 0 8, 0y 0 3, x! #<br />

! y 12V3 q 3<br />

@<br />

0 10, 0v ! 3, a ! !<br />

0m 0 6, 0n 0 6, m! #<br />

! n 6<br />

# b 10.5<br />

0 10, u ! #<br />

! 0 p 0 1, 0 q 0 5, p! #<br />

! q 3 v 50<br />

whose magnitudes are shown in the diagram<br />

below, calculate the dot product.<br />

120°<br />

)b* = 6<br />

)a* = 7.5<br />

9. Use the properties of the dot product to simplify each of the following<br />

expressions:<br />

a. 1a ! 5b ! 2 #<br />

! !<br />

12a 3b 2<br />

b. 3x ! # 1x<br />

!<br />

3y<br />

! 2 1x<br />

! 3y<br />

! 2 # 13x<br />

! y<br />

! 2<br />

NEL<br />

CHAPTER 7 377

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