Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/801803218233753600]problem posted on Twitter[/url] by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] . [br] [br][color=#666666][b]Feel free to change the size of the circles by moving point [i]A[/i] or [i]B[/i].[/b][/color] [br][color=#9900ff][b]Goal:[/b][/color] Prove that [math]FG=\frac{2}{5}\cdot r[/math], where [color=#1e84cc][b][i]r[/i] = the radius of either circle.[/b][/color] [br][br]How can you formally prove what this applet informally illustrates?