1 limx-4 x2-6x+8/x2-5x+4=limx-4 (x-2)(x-4)/(x-1)(x-4)2 y=(x+1)(x-1)/(x-1)（x-2) 3 f(x)=x2(x+3)-(x+3)/(x-2)(x+3)=(x2-1)(x+3)/(x-2)(x+3)=x2-1/x-2;就先写到这，剩下的自己解决，第三个有点乱！
