(1-a²)(1-b²)-4ab 2x²+4xy+2y²-x-y-1 1+x²-y²-2x+2yz 12x²+11xy-15y²-30x+8y+12 a的四次方

① (1-a²)(1-b²)-4ab=1-a²-b²+a²b²-4ab=1-2ab+a²b²-(a²+b²+2ab)=(1-ab)²-(a+b)²=(1-ab-a-b)(1-ab+a+b)② 2x²+4xy+2y²-x-y-1=2(x+y)²-(...