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PROVE THAT sinx+sin3x+sin5x+sin7x=4cosxcos2xsin4x PLZ ANSWER FAST
sinx+sin3x+sin5x+sin7x = sinx+sin7x +sin3x+sin5x
                                        =2sin(7x+x)/2 cos(7x-x)/2 + 2sin(5x+3x)/2 cos(5x-3x)/2
                                        =2sin4x cos3x + 2sin4x cosx
                                        =2sin4x(cos3x + cosx)
                                       =2sin4x 2cos2xcosx (cosC + cosD =2cos (C+D)/2cos(C-D)/2)
                                       =4cosx cos2x sin4x


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