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Unit vectors u and v have direction cosines (1/3, 2/3, 2/3) and (2/3, 1/3, -2/3). What is cos of the angle between them?
A1
B4/9
C-4/9
D0
Answer & Solution
Correct answer: D. 0
The sum is 2/9 + 2/9 - 4/9 = 0, so the lines are perpendicular.
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