Resposta
$(x - h)^2 + (y - k)^2 = r^2$, where $(h, k)$ is the center of the circle and $r$ is the radius ($r > 0$).
Explicação
When given in general form $x^2 + y^2 + Dx + Ey + F = 0$, complete the square for both $x$ and $y$ terms to find the center and radius.