若cos(θ-pai/4)=a,求sin(θ+pai/4)

问题描述:

若cos(θ-pai/4)=a,求sin(θ+pai/4)

cos(θ-pai/4)
=sin(pai/2-θ-pai/4)
=sin(pai/4-θ)=a
sin(θ+pai/4)
=-sin(pai/4-θ)
=-a