cos2x*(1-cos2x)=3sin^2x

cos2x-cos^2x=3sin^2x
cos^2x-sin^2x-(cos^2x-sin^2x)^2=3sin^2x
cos^2x-sin^2x-cos^2x+sin^2x=3sin^2x
3sin^2x=0
sin^2x=0
sinx=0
x=pin