有没有打错符号 xy-x-y-1,请检查一下额，是xy-x-y+1，打错了=[(xy-x)-(y-1)]/(y平方-2y+1)=[x(y-1)-(y-1)]/(y-1)²=(y-1)(x-1)/(y-1)²=(x-1)/(y-1)