(1)x/(x^2+2xy+y^2)与y/(x+y)
x/(x+y)²与y(x+y)/(x+y)²
(2)(x+4)/(x^2+4x)与(x-5)/x(x-5)-2(x-5)
(x+4)/(x^2+4x)=(x+4)/x(x+4)=1/x
(x-5)/x(x-5)-2(x-5)=(x-5)/(x-5)(x-2)=1/(x-2)
通分后是：(x-2)/x(x-2)与x/x(x-2)