6

6. What is the value of c for which the vectors

are orthogonal?

A. -5/7

B. -4/7

C. -3/7

D.-2/7

E. -1/7

Solution: The answer is D

Two vectors are orthogonal means, by definition, that their dot product is 0. So if the two given vectors are orthogonal then

2*4 + 7*c + (c + 2)*(-3) + 3*(c) = 0.

Solving for c we get c = -2/7.