Formula
If the circle equation is: $Ax^2+Ay^2+DX+Ey+F=0$ than the cetrer of the circle has coordinates: $$a = -\dfrac{D}{2A}, ~~~ b = -\dfrac{E}{2A} $$
If the circle equation is: $Ax^2+Ay^2+DX+Ey+F=0$ than the cetrer of the circle has coordinates: $$a = -\dfrac{D}{2A}, ~~~ b = -\dfrac{E}{2A} $$