Question

(sin²x+cos²x)²-2sin²xcos²x=?

Answer 1

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

Answer 2

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