Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/4/p1313-decagon-pentadecagon-equilateral-triangle.htm]post by Antonio Gutierrez[/url] ([url=http://gogeometry.com/]GoGeometry[/url]). [br][br][b][color=#0000ff]How can you formally prove what this applet informally illustrates? [/color][/b]