Creation of this applet was inspired was inspired by a [url=http://www.gogeometry.com/problem/p410_regular_pentagon_diagonal_angle.htm]post[/url] from Antonio Gutierrez ([url=http://www.gogeometry.com/]GoGeometry[/url]). [br][br]Shown below are 2 regular pentagons. [color=#ff00ff][br][br][b]What is the measure of the moving angle? [/b][/color][b][br][br]How can we formally prove what is dynamically illustrated here? [/b]