Circumgon

In mathematics and particularly in elementary geometry, a circumgon is a geometric figure which circumscribes some circle, in the sense that it is the union of the outer edges of non-overlapping triangles each of which has a vertex at the center of the circle and opposite side on a line that is tangent to the circle.[1]: p.

855  The limiting case in which part or all of the circumgon is a circular arc is permitted.

A circumgonal region need not even be a convex polygon: for example, it could consist of three triangular wedges meeting only at the circle's center.

It is these properties that make circumgons interesting objects of study in elementary geometry.

The concept and the terminology of a circumgon were introduced and their properties investigated first by Tom M. Apostol and Mamikon A. Mnatsakanian in a paper published in 2004.