已知x=-2,求（2x）/（x³+2x²+x）÷（x-1）/（x²+x）的值
问题描述：
已知x=-2,求（2x）/（x³+2x²+x）÷（x-1）/（x²+x）的值
答
原式=2x/[x(x+1)²]×x(x+1)/(x-1)
=2/(x+1)²×x(x+1)/(x-1)
=2x/(x+1)(x-1)
=2x/(x²-1)
=-4/(4-1)
=-4/3