解
最简公分母为：2x(x+1)(x-1)
x/(2x+2)=x²(x-1)/[2x(x+1)(x-1)]
1/(x²+x)=2(x-1)/[2x(x+1)(x-1)]
1/(x²-1)=4x/[2x(x+1)(x-1)]