Creation of this applet was inspired by a [url=http://www.gogeometry.com/problem/p773-intersecting-circles-midpoint-secant-plane-geometry.htm]post[/url] from Antonio Gutierrez ([url=http://www.gogeometry.com/]GoGeometry[/url].) [br][br][color=#38761d][b]The green slider adjusts the size of the green circle. [/b][/color][br][color=#666666][b]The gray point[/b][/color] [color=#bf9000][b]adjusts the size of the tan circle. [/b][/color] [br][color=#0000ff][b]Feel free to move the dark blue point anywhere you'd like. [/b][/color][br][br][b][color=#9900ff]How can we formally prove what is informally illustrated here? [/color][/b]