2 Answers Sean Jan 4, 2018 sin3x = 3sinxcos2x −sin3x Explanation: . sin3x = sin(2x + x) = sin2xcosx +cos2xsinx We have double-angle identities: sin2x = 2sinxcosx cos2x = cos2x −sin2x sin3x = 2sinxcosxcosx +(cos2x − sin2x)sinx sin3x = 2sinxcos2x +sinxcos2x −sin3x sin3x = 3sinxcos2x −sin3x Answer link George C. Jan 4, 2018