Answer
$\sqrt[4] (x^{3})$
Work Step by Step
$\sqrt[4] x\times\sqrt x=x^{\frac{1}{4}}\times x^{\frac{1}{2}}$
We can use the product rule to simplify further, which holds that $a^{m}\times a^{n}=a^{m+n}$ (where a is a real number, and m and n are positive integers).
$x^{\frac{1}{4}+\frac{1}{2}}=x^{\frac{1}{4}+\frac{2}{4}}=x^{\frac{3}{4}}=\sqrt[4] (x^{3})$