Circle Equation

This calculator writes the equation of a circle from its centre and radius or from its centre and a point, and finds the centre and radius from the general equation.

(x − a)² + (y − b)² = R²

To get the centre from the general equation x² + y² + Dx + Ey + F = 0, complete the squares in x and y.

Example. x² + y² − 4x + 6y − 12 = 0 becomes (x − 2)² + (y + 3)² = 25: centre (2, −3), radius 5.