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    				| 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` | |