求cosx-cos3x=2sin2xsinx的详细化简过程,
问题描述:
求cosx-cos3x=2sin2xsinx的详细化简过程,
答
cosx-cos3x=cosx-[cos2xcosx-sin2xsinx]
=cosx-cos2xcosx+sin2xsinx
=cosx(1-cos2x)+sin2xsinx
=cosx*2sin^2x+sin2xsinx
=sin2xsinx+sin2xsinx
=2sin2xsinx