(sin^3(a-270)cos(360-a))/(tg^3(a-90)cos^2(a-270))
Пожалуйста, помогите упростить

$frac{sin^3( alpha -270)*cos(360- alpha )}{tg^3( alpha -90)*cos^2( alpha -270)} =$ $frac{-sin^3( 270-alpha)*cos(360- alpha )}{-tg^3( 90-alpha)*cos^2( 270-alpha)} =$ $frac{sin^3( 270-alpha)*cos(360- alpha )}{tg^3( 90-alpha)*cos^2( 270-alpha)} =$ $= frac{-cos^3 alpha *cos alpha }{ctg^3 alpha *sin^2 alpha } = frac{-cos^4 alpha }{ frac{cos^3 alpha }{sin^3 alpha }*sin^2 alpha } = frac{-cos^4 alpha*sin alpha }{cos^3 alpha } =-cos alpha *sin alpha =- frac{1}{2} sin2 alpha$