Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/892105202001600515]tweet[/url] from[url=https://twitter.com/gogeometry] Antonio Gutierrez[/url] (GoGeometry). [br][br]The 2 circles you see are tangent to each other. [br]Feel free to move any of the [b][color=#ff00ff]LARGE PINK POINTS[/color][/b] and/or [b][color=#666666]LARGE GRAY POINT[/color][/b] anywhere you'd like.[br][br][b][color=#9900ff]How can we formally prove what is dynamically illustrated here? [/color][/b]