原式=2x/[(x-2)(x+1)]*(x+1)/(x-1)-x(x+2)/[(x+2)(x-2)]
=2x/[(x-2)(x-1)]-x/(x-2)
=[2x-x(x-1)]/[(x-2)(x-1)]
=-(x²-3x)/(x²-3x+2)