Best Approach

sin7x sin5x sin9x sin3x cos7x cos5x cos9x cos3x = tan 6x. Sol. L.H.S.= sin7x sin5x sin9x sin3x cos7x cos5x cos9x cos3x = 7x 5x 7x 5x 9x 3x 9x 3x 2sin cos 2sin cos 2 2 2 2 7x 5x 7x 5x 9x 3x 9x 3x 2cos cos 2cos cos 2 2 2 2 (Using "C, D" formulae) = 2sin6xcosx 2sin6xcos3x 2cos6xcosx 2cos6xcos3x = 2sin6xcosx cos3x 2cos6xcosx cos3x = sin6x cos6x ... ................
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