x^2-1+y^2-2xy
问题描述：
x^2-1+y^2-2xy
答
原式=(x²-2xy+y²)-1
=(x-y)²-1
=(x-y+1)(x-y-1)
x^2-1+y^2-2xy
原式=(x²-2xy+y²)-1
=(x-y)²-1
=(x-y+1)(x-y-1)