CUET Preparation Today
CUET
-- Mathematics - Section B1
Three-dimensional Geometry
A directed line segment angles α, β, γ with the coordinate axes. The value of ∑ cos 2α is always equal to :
-1
1
-2
2
$\sum \cos 2 \alpha=\sum\left(2 \cos ^2 \alpha-1\right)$
$=2 \sum \ell^2-3$
$=-1$
