Đáp án:
$\begin{array}{l}
\left( {\sqrt[3]{a} + \sqrt[3]{b}} \right)\left( {{a^{\dfrac{2}{3}}} + {a^{\dfrac{2}{3}}} - \sqrt[3]{{ab}}} \right)\\
= \left( {{a^{\dfrac{1}{3}}} + {b^{\dfrac{1}{3}}}} \right)\left( {2{a^{\dfrac{2}{3}}} - {a^{\dfrac{1}{3}}}.{b^{\dfrac{1}{3}}}} \right)\\
= 2a - {a^{\dfrac{2}{3}}}.{b^{\dfrac{1}{3}}} + 2{a^{\dfrac{2}{3}}}.{b^{\dfrac{1}{3}}} - {a^{\dfrac{1}{3}}}.{b^{\dfrac{2}{3}}}\\
= 2a + {a^{\dfrac{2}{3}}}.{b^{\dfrac{1}{3}}} - {a^{\dfrac{1}{3}}}.{b^{\dfrac{2}{3}}}
\end{array}$
(Sau a^1/3 là b^1/3 thì mới có thể rút gọn ra số đẹp)
