原式
=[(3x+4)/(x-1)(x+1) - 2/(x-1) ] * (x-1)²/(x+2)
=(3x+4-2x-2)/(x+1) * (x-1)/(x+2)
=(x-1)/(x+1)
x=-3
原式=(x-1)/(x+1)=(-3-1)/(-3+1)=2