Creation of this applet was inspired by a [url=http://www.gogeometry.com/problem/p751-parallelogram-congruence-angle-bisector-high-school-college.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br][b][color=#1e84cc]You can adjust the size of the (soon-to-appear) interior angle using the slider in the lower left corner. [/color][/b] [br][b]You can also move any of the LARGE POINTS anywhere you'd like AT ANY TIME. [br][/b][br][b][color=#ff00ff]How can we formally prove what is dynamically illustrated here? [/color][/b]