[tex]\bf \textit{equation of a circle}\\\\
(x- h)^2+(y- k)^2= r^2
\qquad
center~~(\stackrel{}{ h},\stackrel{}{ k})\qquad \qquad
radius=\stackrel{}{ r}\\\\
-------------------------------\\\\
(x-3)^2+(y+5)^2=49\implies [x-\stackrel{h}{3}]^2+[y-\stackrel{k}{(-5)}]^2=\stackrel{r}{7^2}\qquad r=7[/tex]
