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If l, m, n are direction cosines of a line, which relation always holds?
Al + m + n = 1
Bl^2 + m^2 + n^2 = 1
Cl x m x n = 1
Dl^2 + m^2 + n^2 = 3
Answer & Solution
Correct answer: B. l^2 + m^2 + n^2 = 1
Squaring and adding the three components over the magnitude gives cos^2a + cos^2b + cos^2c = 1.
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