(3/a-2+12/a平方-4)除(2/a-2 -1/a+2) =[3(a+2)/(a²-4)+12/(a²-4)]÷[2(a+2)/(a²-4)-(a-2)/(a²-4)]=(3a+18)/(a²-4)÷(a+6)/(a²-4)=(3a+18)÷(a+6)=3(a+6)÷(a+6)=3