已知tanx=2,则cos2(x-π/4)=

问题描述:

已知tanx=2,则cos2(x-π/4)=

tanx=2
cosx=五分之根号五
sinx=五分之二乘根号五
cos2(x-π/4)
= cos(2x-π/2)
=cos2x*cosπ/2+sin2x*sinπ/2
=sin2x
=2sinx*cosx
=4/5