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Prove that sinx + sin3x + sin5x + sin7x = 4cos x cos2x sin4x

Answer»

LHS = (sin7x + sin x) + (sin5x + sin3x) 

= 2sin4xcos3x + 2sin4xcosx 

= 2sin4x(cos3x + cosx) 

= 2sin4x2cos2x cos x 

= 4cosxcos2xsin4x 

= RHS. 



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