已知sin(α-π/4)=1/3,则cos(π/4+α)的值等于
问题描述:
已知sin(α-π/4)=1/3,则cos(π/4+α)的值等于
答
cos(π/4+α)
=cos(π/2+α-π/4)
=-sin(α-π/4)
=-1/3