Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/880520149123596289]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]For the two circles shown, both common external tangents are shown.[br]The segments that pass through the[b][color=#ff00ff] two pink points[/color][/b] are tangents to these circles as well. [br][b][color=#0000ff][br]How can we formally prove what this applet informally illustrates? [/color][/b] [br]