cos2a/sin(a-派/4)=-根号2/2,则sin2a=?

cos2a/sin(a-派/4)=-根号2/2,则sin2a=?
cos2a/sin(a-派/4)=-根号2/2,则sin2a=?

cos2a/sin(a-派/4)=-根号2/2,则sin2a=?
cos2a/sin(a-派/4)=-根号2/2,
(cosa-sina)(cosa+sina)/[(√2/2)(sina-cosa)]=-√2/2
cosa+sina=-1/2
sin2a=(sina+cosa)²-1=1/4-1=-3/4