（x-y)/(2x+2y) =(x-y)/2(x+y) =(x-y)(x+y)/2(x+y)^2 xy/(x+y)^2 =2xy/2(x+y)^2 x - y/2x + 2y =(x^2-y+4xy)/2x =(x^2-y+4xy)(x+y)^2/2x(x+y)^2 xy/(x+y)^2 =2x^2y/2x(x+y)^2 不知你的分式是哪种情况.