# GoGeometry Action 168!

- Author:
- Tim Brzezinski

- Topic:
- Geometry

Creation of this resource was inspired by a problem posted by Antonio Gutierrez.
You can move the 2 LARGE WHITE POINTS anywhere you'd like at any time.

**Key Questions:**1) How do we know the octagon shown is a**regular octagon**? Explain. 2) Suppose each side of the octagon has length*a*. How can we write the length of the**purple segment**as a function of*a*? That is, how can we write the length of the**purple segment**in terms of*a*? 3)**How can we formally prove the phenomenon dynamically illustrated here?**