cosx-cos3x如何转化为2sin2x*sinx

分类: 作业答案 • 2022-02-12 11:36:12

问题描述：

答

cosx-cos3x
=cosx-cos2xcosx+sin2xsinx
=cosx(1-cos2x)+sin2xsinx
=2sinxcosxsinx+sin2xsinx
=2sin2xsinx

答

cosx-cos3x
=cos(2x-x)-cos(2x+x)
=(cos2xcosx+sin2xsinx)-(cos2xcosx-sin2xsinx)
=2sin2xsinx