Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/842366978505490432]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br][b][color=#0000ff]How can you formally prove what this applet informally illustrates? [/color][/b] [br][br](Note: The [b][color=#38761d]smaller green circle[/color][/b] is also tangent to the two quarter circles.)