1.约分：a²-3a+2/a²-4a+3 2.化简：（1）3+2x-x²/x²-7x+12 （2）二分之一x3.如果x/2=y/3=z/4≠0，那么x+y+z/x+y+z的值是：A .7 B.8 C.9 D.10

(a^2-3a+2)/(a^2-4a+3)=(a-2)(a-1)/[(a-3)(a-1)]=(a-2)/(a-3)
(3+2x-x^2)/(x^2-7x+12)=-(x-3)(x+1)/[(x-3)(x-4)]=-(x+1)/(x-4)=(x+1)/(4-x)

1、a²-3a+2/a²-4a+3 =(a-1)(a-2)/[(a-1)(a-3)]=(a-2)/(a-3)
2、3+2x-x²/x²-7x+12 =-(a-3)(a+1)/[(a-3)(a+4)]=-a+1/a+4

1、a²-3a+2/a²-4a+3 =（a-2)(a-1)/(a-3)(a-1)=（a-2)/(a-3)
2 、 3+2x-x²/x²-7x+12 =-(x-3)(x+1)/(x-3)(x-4)=-(x+1)/(x-4)

1、a²-3a+2/a²-4a+3=(a-1)(a-2)/（a-1)(a-3）=(a-2)/（a-3）
(1)、3+2x-x²/x²-7x+12=(3-x)(1+x)/(x-3)(x-4)=(1+x)/(4-x)
(2)、