# GoGeometry Action 135!

- Author:
- Tim Brzezinski

Creation of this applet was posed by a problem posted by Antonio Gutierrez (GoGeometry).
Note the quadrilateral below is split into 2 triangles. The incircles of both triangles are shown.
The

**blue points**are points of tangency. Slide the slider carefully and observe what happens. Then, answer question (1) below.**How can we formally prove what is dynamically illustrated here?**## 1.

Suppose the 4 sides of this quadrilateral have lengths p, q, r, and s. Express the distance between the 2 **blue points** in terms of p, q, r, and s.