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For two lines with direction cosines l1, m1, n1 and l2, m2, n2, cos θ equals:
A|l1+l2| + |m1+m2| + |n1+n2|
B|l1l2 + m1m2 + n1n2|
C|l1m2 + m1n2 + n1l2|
Dl1l2 x m1m2 x n1n2
Answer & Solution
Correct answer: B. |l1l2 + m1m2 + n1n2|
The cosine of the acute angle is the absolute value of the dot product of the two unit vectors.
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