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

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Answer 1 · 2014-09-14T13:56:27

The general form of a circle looks like ...

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

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

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

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

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

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

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