（x+y-2XY)(x+y-2)+(xy-1)^2=[（x+y)-2xy][(x+y)-2]+(xy-1)^2=(x+y)^2-2(xy+1)(x+y)+4xy+x^2y^2-2xy+1=(x+y)^2-2(xy+1)(x+y)+x^2y^2+2xy+1=(x+y)^2-2(xy+1)(x+y)+(xy+1)^2=[(x+y)-(xy+1)]^2=(x+y-xy-1)^2=[x(1-y)-(1...