Chapter 10 - Section 10.2 - Limits and Continuity - Exercises - Page 707: 23

$f(0)=-1$ makes the function continuous at $x=0$.

Graphing (see image below), and creating a table where values approach $x=a$ from either side, we see that $f(0)$ is undefined, but function values approach $-1$, as $x$ approaches $a=0,$ both from the left and the right. So, placing $f(0)=-1$ makes the function continuous at $x=0$.