原式=x²(x+y)/y(x+y)(x-y)-x(x-y)/x(x+y)-2xy/(x+y)(x-y)=(x³+x²y-x³+2x²y-xy²-2xy²))/y(x+y)(x-y)=(3x²y-3xy²))/y(x+y)(x-y)=3xy(x-y)/y(x+y)(x-y)=3x/(x+y)