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The lines with direction vectors i + 2j + 2k and 3i + 2j + 6k have cos θ equal to:
A19/42
B19/63
C17/21
D19/21
Answer & Solution
Correct answer: D. 19/21
The dot product is 3 + 4 + 12 = 19 and the magnitudes are 3 and 7, giving 19/21.
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