x²y+xy²-xy=xy(x+y+1)a²-b²+a+b=(a+b)(a-b)+(a+b)=(a+b)(a-b+1)25(a+b）²-（a+b)²=24(a+b)²(x²+y²）²-4x²y²=(x²+y²-2xy)(x²+y²+2xy)=(x-y)²(x+y)²8a³-2a（a+1）²=2a(4a²-(a+1)²)=2a(2a+a+1)(2a-a-1)=-2a(3a+1)(a-1)
