Question

sin^2(-a)-sin^4(-a)/cos^2(-a)

Answer 1

$\frac{sin^2(-\alpha)-sin^4(-\alpha)}{cos^2(-\alpha) }=\frac{sin^2(-\alpha)(1-sin^2(-\alpha))}{cos^2(-\alpha) }=\\\\\frac{sin^2(-\alpha) cos^2(-\alpha))}{cos^2(-\alpha) }=sin^2(-\alpha) =sin^2\alpha$