Example 3 - THe WHOLE STORY
GeoGebra
The  film of the steps how to use the applet without comments.

The  film of the steps how to use the applet but now with commentary.

 
This is a Java Applet created using GeoGebra from www.geogebra.org - it looks like you don't have Java installed, please go to www.java.com

Here is the corresponding    file to start with.

Other approaches