∵2xy/(x+y)^2的分母是(x+y)^2
x/(x^2-y^2)的分母是x^2-y^2=(x+y)(x-y)
∴它们的公分母是(x-y)(x+y)^2
故它们通分后分别是：2xy/(x+y)^2=2xy(x-y)/[(x-y)(x+y)^2]
x/(x^2-y^2)=x(x+y)/[(x-y)(x+y)^2].