sin2xcos3x等于sin5x-sinx

投稿:素年凉音 优质问答领域创作者 发布时间:2023-10-04 08:09:46
sin2xcos3x等于sin5x-sinx

答:sin2xcos3x≠sin5x-sinx。

根据公式sinacosb=1/2(sin(a+b)+sin(a-b))得

sin2xcos3x=1/2(sin(2x+3x)+sin(2x-3x))

                    =1/2(sin5x+sin(-x))

                     =1/2(sin5x-sinx)

也可见下图:

sin2xcos3x等于sin5x-sinx

①sin2xcos3x

=1/2(2sin2xcos3x)

=1/2(sin2xcos3x+sin2xcos3x

+cos2xsin3x-cos2xsin3x)

=1/2[(sin2xcos3x+cos2xsin3x)-(cos2xsin3x-sin2xcos3x)

=1/2(sin5x-sinx)

②sin2xcos3x

=1/2(2sin2xcos3x)

=1/2(sin2xcos3x+sin2xcos3x

+cos2xsin3x-cos2xsin3x)

=1/2[(sin2xcos3x+cos2xsin3x)-(cos2xsin3x-sin2xcos3x)]

=1/2(sin5x-sinx)