2x/（x³+2x²+x）除以（x-1）/（x²+x）
=2x/x(x+1)²*(x²+x)/(x-1)
=2/(x+1)²*x(x+1)/(x-1)
=2x/(x+1)(x-1)
=2x/(x²-1)
=2×(-2)/(4-1)
=-4/3