Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/4/p1354-circle-tangent-secante-parallel-tutoring.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][color=#1e84cc][b]How can we formally prove what is dynamically illustrated here? [/b][/color]