Question

sin^4 a -sin^2a=cos^4a-cos^2a

Answer 1

$sin^4 alpha -sin^2 alpha =cos^4 alpha -cos^2 alpha \ sin^2 alpha (sin^2 alpha -1)=cos^2 alpha (cos^2 alpha -1)\ sin^2 alpha *(-cos^2 alpha )=cos^2 alpha (-sin^2 alpha )\ -sin^2 alpha cos^2 alpha =-sin^2 alpha cos^2 alpha \ -sin^2 alpha cos^2 alpha-(-sin^2 alpha cos^2 alpha )=sin^2 alpha cos^2 alpha -sin^2 alpha cos^2 alpha =0\ 0=0$