check the picture below.
[tex]\bf \textit{equation of a circle}\\\\
(x-{{ h}})^2+(y-{{ k}})^2={{ r}}^2
~~
\begin{array}{lllll}
center~(&\quad {{ h}},&\quad {{ k}}\quad )\qquad
radius=&{{ r}}\\
&-\sqrt{5}&-\sqrt{5}&\sqrt{5}
\end{array}
\\\\\\\
[x-(-\sqrt{5})]^2+[y-(-\sqrt{5})]^2=(\sqrt{5})^2
\\\\\\
(x+\sqrt{5})^2+(y+\sqrt{5})^2=5[/tex]
