#### Answer

$|z|$

#### Work Step by Step

As shown on page 437, $\sqrt[n] a^{n}=|a|$ when $n$ is an even positive integer.
In this case, we know that $\sqrt (-z)^{2}$ is equivalent to $\sqrt[2] (-z)^{2}$, since we are taking the square root.
Therefore, we know that $\sqrt (-z)^{2}=\sqrt[2] (-z)^{2}=|-z|=|z|$.