CirclesInCircle.nod is an assemblage of nodes that places "n" number of circles (of unknown radius "r"), inside of a big circle of given radius R.
The equations could be adjusted to find R, given r.

Math geometry credit to brynn, 2019, Inkscape forum.

Circumscribed Polygon of "n" sides may be placed with the side center points coinciding with the small circle centers.
The apothem of the polygon is the radius3 from the big circle center, to one of the said side center points.

- Brian