a²-5a+6/a²-1÷a-3/a²+a-2-a²-4/a+3=（a-2）(a-3)/(a+1)(a-1)÷（a-3）/(a-1)(a+2)-(a²-4)/(a+3)=(a-2)(a+2)/(a-3)-(a²-4)/(a+3)=(a²-4)[1/(a-3)-1/(a+3)]=(a²-4)*-6/(a
...（a-2)(a+2)/(a-3)不是（a-2)(a+2)/(a+1)（a-2)(a+2)=a²-4呀后面也有a²-4提出来