Creation of this applet was inspired by a [url=http://www.gogeometry.com/problem/p282_right_triangle_cevian_angles_congruence.htm]problem posted[/url] by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br][b][color=#ff00ff]You can alter the size of the pink angle by using the pink slider.[/color][/b] [br][br][b][color=#9900ff]How can we formally prove the relationship dynamically illustrated here? [/color][/b]