If cos ⁡ , cos ⁡ , cos ⁡ are the direction cosines of a vector a, then cos ⁡2 + cos ⁡2 + cos ⁡2 is equal to

Question

Accepted Answer

Correct answer: C. (c) : We have, cos ⁡2 + cos ⁡2 + cos ⁡2 =2 cos^2 ⁡ -1+2 cos^2 ⁡ -1+2 cos^2 ⁡ -1 =2( cos^2 ⁡ + cos^2 ⁡ + cos^2 ⁡ )-3 =2 1-3 ( ∵ cos^2 ⁡ + cos^2 ⁡ + cos^2 ⁡ =1) =2-3=-1

$If cos α, cos β, cos γ are the direction cosines of a vector a, then cos 2 α + cos 2 β + cos 2 γ is equal to$

Solution

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