Answer
$\frac{1}{3}$
Work Step by Step
According to the textbook, a number, $a$, is a square root of another number, $b$, if $a^2=b$.
$(\frac{1}{3})^2=\frac{1}{9}$, so $\frac{1}{3}$ is a square root of $\frac{1}{9}$.
Therefore: $\sqrt {\frac{1}{9}}=\frac{1}{3}$
