Determining Range

Question

$X_i\sim^{iid}N(0,1);\quad i=1,2$

so $x_i$ ranges from $-\infty$ to $\infty$.

Now $Y=X_1^2+X_2^2$

so $y$ ranges from $0$ to $\infty$.

But how $Z=X_2$ is ranges from ($-\sqrt y$) to $\sqrt y$ ?