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Grade 11,

Question belongs to trigonometry.......of class 11th

Question belongs to trigonometry.......of class 11th

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Grade:11

1 Answers

Arun
25750 Points
6 years ago
Dear Narendra
 
As you know
 cos²A - sin²A = cos2A
Hence
The LHS expression becomes 
Cos 2(theta - phi)/2 = cos (theta - phi)
= Cos theta* cos phi + sin theta * sin phi
 
Hence I think you have forgotten the correct RHS.
 
Regards
Arun (askIITians forum expert)

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