Question

If α, β and γ are the direction cosine of the line then cos²α + cos²β + cos²γ = ____

(A) 1

(B) – 1

(C) (4/3)

(D) – (4/3)

Answer 1

The correct option (B) – 1

Explanation:

 α, β, γ are direction cosines of line.

cos²α + cos²β + cos²γ = 1

∴ [(1 + cos2α)/2] + [(1 + cos2β)/2] + [(1 + cos2γ)/2] = 1

∴ cos2α + cos2β + cos2γ = – 1.