(5-xy/x^3-x^2y)/(1-5/xy)^2*(y-x)^3
=-(x-y)^3[-(xy-5)/x^2(x-y)]/[(xy-5)/xy]
=(x-y)^3(xy-5)xy/x^2(x-y)(xy-5)
=y(x-y)^2/x