已知sin(a-pai/4)=1/3,则cos(a+pai/4)=?

已知sin(a-pai/4)=1/3,则cos(a+pai/4)=?
已知sin(a-pai/4)=1/3,则cos(a+pai/4)=?

已知sin(a-pai/4)=1/3,则cos(a+pai/4)=?
sin(a-π/4)
=sin[(a+π/4)-π/2]
=-sin[π/2-(a+π/4)]
=-cos(a+π/4)
=1/3
cos(a+π/4)=-1/3