`\text{~~Holi~~}`
`(y/(x^2-xy)-x/(xy-y^2)):(x+y)/(x^2y-xy^2)`
`= (y/(x(x-y))-x/(y(x-y))).(x^2y-xy^2)/(x+y)`
`= (y^2-x^2)/(xy(x-y)).(xy(x-y))/(x+y)`
`= ((y+x)(y-x))/(xy(x-y)).(xy(x-y))/(x+y)`
`= (-(y+x)(x-y))/(xy(x-y)).(xy(x-y))/(x+y)`
`= (-y-x).(x-y)/(x+y)`
`= -(y+x).(x-y)/(x+y)`
`= -1.(x-y)`
`= -(x-y)`
`= -x+y`