Answer
$\frac{\sqrt{3}}{3}$
Work Step by Step
When the denominator has a square root (i.e. $\sqrt{a}$), we multiply the numerator and denominatory by $\sqrt{a}$:
$\frac{1}{\sqrt{3}}=\frac{1}{\sqrt{3}}\cdot\frac{\sqrt{3}}{\sqrt{3}}=\frac{\sqrt{3}}{3}$
