How do I find the radius of a circle from its general equation?

Sep 14, 2014

The general form of a circle looks like ...

${x}^{2} + {y}^{2} + A x + B y + C = 0$

In the standard form to the equation for a circle look like ...

${\left(x - h\right)}^{2} + {\left(y - k\right)}^{2} = {r}^{2}$

$\sqrt{{r}^{2}} = r ,$radius

Convert the general form to standard form by using the completing the square process.

You will then have the ${r}^{2}$ value.

The square root of ${r}^{2}$ is the radius of the circle.