so hmm notice the picture below
you have the center, and a point on the circle... all you need is the radius
[tex]\bf \textit{distance between 2 points}\\ \quad \\
\begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
&({{ 1}}\quad ,&{{ -2}})\quad
% (c,d)
&({{ 3}}\quad ,&{{ -4}})
\end{array}\qquad
% distance value
d = \sqrt{({{ x_2}}-{{ x_1}})^2 + ({{ y_2}}-{{ y_1}})^2}\leftarrow r[/tex]
then use that radius in the circle's equation
[tex]\bf (x-{{ h}})^2+(y-{{ k}})^2={{ r}}^2
\qquad center\ ({{ h}},{{ k}})\qquad
radius={{ r}}[/tex]
