Question 613414
how do you prove that 1/4(sin4x) = sinx(cosx^3)-cosx(sinx^3)
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Start with left side:
1/4(sin4x)
=1/4[2sin2xcos2x]
=1/2[2sixcosx(cos^2x-sin^2x)
=sinxcos^3x-cosxsin^3x
Verified: 
left side=right side