Question

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

Answer 1

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