Question

(Sina-cosa)^2/sin^4a+2sin^2acos^2a+cos^4a=1-sin2a

Answer 1

$frac{(sina-cosa)^2}{sin^4a+2sin^2acos^2a+cos^4a}=frac{sin^2a-2sinacosa+cos^2a}{(sin^2a+cos^2a)^2}=1-sin2a$