Bankoff Circle

$\begin{figure}\begin{center}\BoxedEPSF{BankoffCircle.epsf}\end{center}\end{figure}$

In addition to the Archimedes' Circles

and

in the Arbelos figure, there is a third circle

congruent to these two as illustrated in the above figure.

See also Arbelos

References

Bankoff, L. ``Are the Twin Circles of Archimedes Really Twins?'' Math. Mag. 47, 214-218, 1974.

Gardner, M. ``Mathematical Games: The Diverse Pleasures of Circles that Are Tangent to One Another.'' Sci. Amer. 240, 18-28, Jan. 1979.