Three
Tangent Circles Theorem: Common Tangents & Concurrent Point.
Level: High
School, SAT Prep, College

The common tangents of three mutually
tangential circles A,
B, and C taken in pairs are concurrent in the point P. P is the
incenter of triangle ABC (center of the incircle).

Dynamic Geometry: You can alter the figure above
dynamically in order to test and prove (or disproved)
conjectures and gain mathematical insight that is less
readily available with static drawings by hand.

This page uses the
TracenPoche
dynamic geometry software and requires
Adobe Flash player 7 or higher.
TracenPoche is a project of Sesamath, an association of French
teachers of mathematics.

Instruction to explore the
theorem above:

Animation. Click the red
button
to start/stop animation

Manipulate. Drag points A
and C to change the figure.

Step by Step construction.
Press P and click the left mouse
on any free area to show the
step-by-step bar and start the
construction:

Hide the step-by-step bar by
using again the combination P +
click left mouse.