sin2x-cos2x=根号2·sin(2x-π/4)?怎么变的

问题描述:

sin2x-cos2x=根号2·sin(2x-π/4)?怎么变的

sin2x-cos2x=根号2*(sin2xcos45-cos2xsin45)=根号2*sin(2x-45)

sin2x-cos2x=根号2·(sin2x·根号2/2-cox2x·根号2)
=根号2·(sin2x·cosπ/4-cos2x·sinπ/4)
=根号2·sin(2x-π/4)(逆用差角的正弦公式)