=(x+2y) (x-2y)-2xy(x2+2y)/2xy=x2-4y2-x2-2y=-4y2-2y
(2yx)(x-2y)-(2x³y/2xy+4xy²/2xy)=2x²y-4xy²-(x²+2y)=2x²y-4xy²-x²-2y
