Asked by Anonymous

If the vectors u and v determine an angle of 60° and |u|=5, u • v = 15, then the value of 2v • (3u - v) equals:

Answers

Answered by oobleck
u•v = |u| |v| cos60°, so
5|v|/2 = 15
|v| = 6
Now you have
2v•(3u-v) = 2v•3u - 2v•v = 6v•u - 2v•v = 6*15 - 2*36 = 18
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