Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/873405683202392065]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br]Below, you will find a circle inscribed in a square. [br](You can move the vertices of the square around if you'd like.) [br][br][b]Slide the slider slowly and carefully observe what happens. [/b][br][br][b][color=#38761d]How does this applet informally show that the area of the green triangle is 1/40 the area of the square? [/color][/b][color=#38761d][b]How can we formally prove this true? [/b][/color]