Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/839464499111424000]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url]. [br][br]The quadrilateral shown below is a rhombus. [br]Lots of properties of a rhombus are shown at first.[br][br][b][color=#ff00ff]What is the measure of the pink angle? [/color][/b] [br][color=#0000ff][b]How can you formally prove the phenomena displayed at the end? [/b][/color]