Finding an equation of circle which passes through three points How to find the equation of a circle which passes through these points $(5,10), (-5,0),(9,-6)$
using the formula 
$(x-q)^2 + (y-p)^2 = r^2$.
I know i need to use that formula but have no idea how to start, I have tried to start but don't think my answer is right.

$\begin{vmatrix}  
x^2+y^2&x&y&1\\
5^2+10^2&5&10&1\\
(-5)^2+0^2&-5&0&1\\
9^2+(-6)^2&9&-6&1\\
\end{vmatrix}=
\begin{vmatrix}  
x^2+y^2&x&y&1\\
125&5&10&1\\
25&-5&0&1\\
117&9&-6&1\\
\end{vmatrix}
=
0$
