x2+y2-x2y-4xy-1因式分解
问题描述：
x2+y2-x2y-4xy-1因式分解
答
是-x²y²
原式=(x²-2xy+y²)-(x²y²+2xy+1)
=(x-y)²-(xy+1)²
=-(xy+1+x-y)(xy+1-x+y)