Докажите:sin^4a+cos^4a-sin^6a-cos^6a=sin^2a*cos^2a

[latex]sin^4 alpha +cos^4 alpha -sin^6 alpha -cos^6 alpha =sin^4 alpha +cos^4 alpha -(sin^6 alpha +cos^6 alpha )=\ \ =sin^4 alpha +cos^4 alpha -(sin^2 alpha +cos^2 alpha )(sin^4 alpha -sin^2 alpha cos^2 alpha +cos^4 alpha )=\ \ =sin^4 alpha +cos^4 alpha -sin^4 alpha -cos^4 alpha +sin^2 alpha cos^2 alpha =sin^2 alpha cos^2 alpha [/latex]Что и требовалось доказать.