You can say that the center is an arbitrary point at (x0, y0)
The distance from each point to the center is the same
d^2 = (x-x0)^2 + (y-y0)^2
Plug in each point into this equation (plug into x and y) and you have a 3x3 system that you can solve for x0 y0 which is the center and d which is the radius. Then you have the equation by putting these constants into the above equation.
