(xy-x^2)÷x^2-2xy+y^2/xy*x-y/y^2*yx^-2(xy-x^2)÷{x^2-2xy+y^2/xy}*{x-y/y^2}*{yx^-2}

(xy-x^2)÷x^2-2xy+y^2/xy*x-y/y^2*yx^-2(xy-x^2)÷{x^2-2xy+y^2/xy}*{x-y/y^2}*{yx^-2}
(xy-x^2)÷x^2-2xy+y^2/xy*x-y/y^2*yx^-2
(xy-x^2)÷{x^2-2xy+y^2/xy}*{x-y/y^2}*{yx^-2}

(xy-x^2)÷x^2-2xy+y^2/xy*x-y/y^2*yx^-2(xy-x^2)÷{x^2-2xy+y^2/xy}*{x-y/y^2}*{yx^-2}
(xy-x^2)÷x^2-2xy+y^2/xy*x-y/y^2*yx^-2
=[x^2y(y-x)÷(y-x)^2]{y(x-y)/x^2y^2}
=[x^2y][y(x-y)]/(y-x)(xy)^2
=(xy)^2(x-y)/[-(x-y)(xy)^2]
=-1

后面应该有括号吧