## Precalculus (6th Edition) Blitzer

$x^2+y^2=9$ See graph.
Step 1. Using $r^2=x^2+y^2$, we have $x^2+y^2=3^2$ or $x^2+y^2=9$ Step 2. We can identify the above equation as a circle with center $(0,0)$ and radius $r=3$ Step 3. See graph.