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Question

If cosα,cosβ,cosγ are the direction cosines of a vector a, then cos2α+cos2β+cos2γ is equal to 
  1. 2  
  2. 3    
  3. 1   
  4. 0    


Solution

The correct option is C 1   
Since  cosα,cosβ,cosγ are direction cosines of vector a,
cos2α+cos2β+cos2γ=1  
Now, cos2α+cos2β+cos2γ
     =(2cos2α1)+(2cos2β1)+(2cos2γ1)
     =2(cos2α+cos2β+cos2γ)3
     =2×13=1

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