X³-X²/X²-X + 1-X²/X+1 - X+2/X²-4
=x2(x-1)/x(x-1)+(1-x)(1+x)/(x+1)-(x+2)/(x+2）(x-2）
=x+（1-x)-1/(x-2)
=1-1/(x-2)
(x-3)/(x-2)