#### Answer

$x^{\frac{5}{9}}$

#### Work Step by Step

The exponent of $x$ (which is 5) is lower then the index (9).
This means that the radical is already in simplest form.
RECALL:
$\sqrt[n]{a^m} = a^{\frac{m}{n}}$
Thus,
$\sqrt[9]{x^5} = x^{\frac{5}{9}}$