（a的3/4次方-8a的3分之一次方b）/（4b的3/2次方+2的3次根号下ab+a的2/3次方）÷（1-2×3次根号下b/a）×（3次根号下a）

你的题目里第一项a^(3/4)可能是a^(4/3)之误.下面按a^(4/3)计算,如果不这样,结果没那么简单.
[a^(4/3)-8ba^(1/3)]/[4b^(3/2)+2(ab)^(1/3)+a^(2/3)]÷[1-2×(b/a)^(1/3)]×a^(1/3)
=[a^(3/4)-8ba^(1/3)]a^(1/3)/{[4b^(3/2)+2(ab)^(1/3)+a^(2/3)][1-2×(b/a)^(1/3)]}
=[a^(4/3)-8ba^(1/3)]a^(2/3)/{[4b^(3/2)+2(ab)^(1/3)+a^(2/3)][a^(1/3)-2b^(1/3)]}
=(a²-8ba)/{[(a^(1/3)]³-[2b^(1/3)³]}
=a(a-8b)/(a-8b)=a
如果你写的题目没错,那么最后=a[a^(5/12)+8b]/(a-8b)