Given three mutually tangent Circles, there exist exactly two nonintersecting Circles Tangent to all three Circles. These are called the inner and outer Soddy Circles, and their centers are called the inner and outer Soddy points. The outer Soddy circle is the solution to the Four Coins Problem. The center of the inner Soddy circle is the Equal Detour Point, and the center of the outer Soddy circle is the Isoperimetric Point (Kimberling 1994).

**References**

Kimberling, C. ``Central Points and Central Lines in the Plane of a Triangle.'' *Math. Mag.* **67**, p. 181, 1994.

© 1996-9

1999-05-26