Question

(cos2a-cos^2a)/1cos^2a

Answer 1

$\frac{\cos2\alpha-\cos^2\alpha}{1-\cos^2\alpha}=\frac{\cos^2\alpha-\sin^2\alpha-\cos^2\alpha}{\sin^2\alpha+\cos^2\alpha-\cos^2\alpha}=\frac{-\sin^2\alpha}{\sin^2\alpha}=-1$