Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/2/p1107-triangle-circumcircle-circle-congruence-math-tutor.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]You can move [b]ANY LARGE POINT[/b] anywhere you'd like[b] AT ANY TIME.[/b] [br][br][b][color=#9900ff]How can we formally prove the phenomenon dynamically illustrated here? [/color][/b]