Answer
$x\cdot\sqrt[3]{a^{3}+b^{3}}$
Work Step by Step
... Radical of a product: $\sqrt[n]{a\cdot b}=\sqrt[n]{a}\cdot\sqrt[n]{b}$
$\sqrt[3]{x^{3}\cdot(a^{3}+b^{3})}=\sqrt[3]{x^{3}}\cdot\sqrt[3]{(a^{3}+b^{3})}$
... if n is odd, $\sqrt[n]{x^{n}}=x$...
... there is no formula to simplify the second factor...
$=x\cdot\sqrt[3]{(a^{3}+b^{3})}$
