（x+y-xy-1)^2=(x-1)^2(y-1)^2（x+y-xy-1)^2这步是怎么变到(x-1)^2(y-1)^2这步的?

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（x+y-xy-1)^2=(x-1)^2(y-1)^2（x+y-xy-1)^2这步是怎么变到(x-1)^2(y-1)^2这步的?
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（x+y-xy-1)^2=(x-1)^2(y-1)^2（x+y-xy-1)^2这步是怎么变到(x-1)^2(y-1)^2这步的?
（x+y-xy-1)^2=(x-1)^2(y-1)^2
（x+y-xy-1)^2这步是怎么变到(x-1)^2(y-1)^2这步的?

（x+y-xy-1)^2=(x-1)^2(y-1)^2（x+y-xy-1)^2这步是怎么变到(x-1)^2(y-1)^2这步的?
（x+y-xy-1)^2
=(x(1-y)-(1-y))^2
=((x-1)(1-y))^2
=(x-1)^2(1-y)^2
=(x-1)^2(y-1)^2

x+y-xy-1=-(x-1)(y-1）
由于是2次方所以负号可以不管了
而(ab)^2=a^2*b^2所以。。

x+y-xy-1=(x-xy)+(y-1)=-x(y-1)+(y-1)=-(x-1)*(y-1)
平方即可得到(x-1)^2(y-1)^2

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