自觉得,觉得前面a多一个平方(a-4)/(3a+24)÷[(a²-4a)/(a²+7a-8)] +1/(3a)=(a-4)/[3(a+8)]×[(a+8)(a-1)]/[a(a-4)]+1/(3a)=1/3×(a-1)/a+1/(3a)=(a-1)/(3a)+1/(3a)=a/(3a)=1/3