cos(x-π/2)=3/5.则cos2x=
问题描述：
cos(x-π/2)=3/5.则cos2x=
答
cos(x-π/2)=sinx=3/5
cos2x=1-2sin^2x=1-2*(3/5)^2=1-18/25=7/25
答
sinx=cos(x-π/2)=3/5
cos2x=1-2sin^2(x)
=1-18/25
=7/25