1.

If a line makes angle `alpha, beta` and `gamma` with the coordinate axes respectively, then `cos2alpha+cos 2 beta+cos 2gamma=`A. 2B. -1C. 1D. 2

Answer» Correct Answer - B
We have
`l=cos alpha, cosb` and `n=cos gamma`
`:.l^(2)+m^(2)+n^(2)=1`
`impliescos^(2) alpha+cos^(2)beta+cos^(2)gamma=1`
`implies(1+cos 2alpha)/2+(1+cos 2 beta)/2+(1+cos 2gamma)/2=1`
`impliescos 2 alpha+cos 2 beta+cos 2gamma=-1`


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