(x^2-2xy)/(x^2-3xy+2y^2)-(xy+y^2)/(x^2-y^2)
=x(x-2y)/(x-2y)(x-y)-y(x+y)/(x-y)(x+y)
=x/(x-y)-y/(x-y)
=(x-y)/(x-y)
=1算了，谢啦