x+y-1=xy/(x+y-xy)
(x+y-1)(x+y-xy)=xy
(x+y)²-(xy+1)(x+y)+xy=xy
(x+y)²-(xy+1)(x+y)=0
(x+y)[(x+y)-(xy+1)]=0
(x+y)(x+y-xy-1)=0好像没化简完、、嗯，是的。继续：
x+y-1=xy/(x+y-xy)
(x+y-1)(x+y-xy)=xy
(x+y)²-(xy+1)(x+y)+xy=xy
(x+y)²-(xy+1)(x+y)=0
(x+y)[(x+y)-(xy+1)]=0
(x+y)(x+y-xy-1)=0
(x+y)[(x-xy)+(y-1)]=0
(x+y)[x(1-y)-(1-y)]=0
(x+y)(1-y)(x-1)=0
(x+y)(x-1)(y-1)=0