sin^4x-cos^4y=sin^2x-cos^2x доказать тождество

sin^4x-cos^4y=sin^2x-cos^2y(sin^2x-cos^2y)(sin^2x+cos^2y)=sin^2x-cos^2ysin^2x-cos^2y*1=sin^2x-cos^2ysin^2x-cos^2y=sin^2x-cos^2y