原式=2xy/(x^2-y^2)+y/(y-x)+x/(x+y) =2xy/(x+y)(x-y)+y(x+y)/(x+y)(x-y)+x(x-y)/(x+y)(x-y) =2xy+xy+y^2+x^2-xy/(x+y)(x-y) =(x+y)^2/(x+y)(x-y) =(x+y)/(x-y)
