вот решение,правда почерк...
sin^2/sin^2/cos^2 + cos^2/cos^2/sin^2 - 2sin^2
(sin^2(cos^2/sin^2) + cos^2(sin^2/cos^2) )/ sin^2/cos^2 * cos^2/sin^2 - 2sin^2
cos^2 + sin^2 - 2sin^2=cos^2-sin^2
