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Questions  

If a line makes acute angles α,β,γ with the coordinate axes such that cosαcosβ=16;  cosβcosγ=123;  cosγcosα=132then , 3cosα+cosβ+cosγ2=2+3+6+λ then λ=

a
6
b
7
c
8
d
9

detailed solution

Correct option is D

If  α,β,γare the angles made by a line with axes then cos2α+cos2β+cos2γ=1Consider,   3cosα+cosβ+cosγ2             =3cos2α+cos2β+cos2γ+2cosαcosβ+2cosβcosγ+2cosγcosα=31+26+223+232=3+6+3+2Therefore,  λ=3⇒λ=9

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