## Algebra 2 (1st Edition)

$$x^2+y^2=9$$
Since the center is at the origin, we use the distance formula to find that the radius must be: $$\sqrt{\left(0-0\right)^2+\left(3-0\right)^2}=3$$ Thus, it follows: $$x^2+y^2=r^2$$ $$x^2+y^2=9$$