Question

(sin²x+cos²x)²-2sin²xcos²x=?

Answer 1

$(\sin^2x+\cos^2x)^2-2\sin^2x\cdot\cos^2x=\sin^4x+2\sin^2 x\cdot\cos^2 x+\cos^4x-\\\\-2\sin^2x\cdot\cos^2x=\sin^4x+\cos^4x$

Answer 2

$(sin^2x+cos^x)^2-2sin^2xcos^2x=\\=sin^4x+2sin^2xcos^2x+cos^4x-2sin^2xcos^2x=sin^4x+cos^4x$