# How do you write the equation for a circle with Center of circle (-3,9) radius with endpoint (0,7)?

${\left(x + 3\right)}^{2} + {\left(y - 9\right)}^{2} = 13$
Standard equation for circle center $\left(a , b\right)$, radius $r$ is ${\left(x - a\right)}^{2} + {\left(y - b\right)}^{2} = {r}^{2}$. The radius $r$ is the distance from the origin to the end point of the radius, which by Pythagoras is $\sqrt{{\left(- 3 - 0\right)}^{2} + {\left(9 - 7\right)}^{2}} = \sqrt{13}$.