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Direction cosines (l, m, n) of a line satisfy:
Al = m = n
Bl² + m² + n² = 1 (unit vector property)
CAlways 0
Dl + m + n = 1
Answer & Solution
Correct answer: B. l² + m² + n² = 1 (unit vector property)
Direction cosines: cosines of angles the line makes with x, y, z axes. (l, m, n) form a unit vector along the line; hence l² + m² + n² = 1.
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