这个算是没有乘以a^(1/3)
所以
[a^(4/3)-8a^(1/3)b]/[4b^(2/3)+2(ab)^(1/3)+a^(2/3)]÷[1-2(b/a)^(1/3)]*a^(1/3)
=a^(2/3)×a^(1/3)
=a
