The routine returns the radius of the given circle c.

The command with(geometry,radius) allows the use of the abbreviated form of this command.

$\mathrm{with}\left(\mathrm{geometry}\right)\:$

$\mathrm{circle}\left(\mathrm{ABC}\,\left[\mathrm{point}\left(A\,0\,0\right)\,\mathrm{point}\left(B\,2\,0\right)\,\mathrm{point}\left(C\,1\,3\right)\right]\right)\:$

$\mathrm{circle}\left(c\,x^2+y^2=9\,\left[x\,y\right]\right)\:$

$\mathrm{radius}\left(\mathrm{ABC}\right)$

$\frac{\sqrt{25}\sqrt{9}}{9}$

$\mathrm{radius}\left(c\right)$

$\sqrt{9}$