GoGeometry Action 97!

Creation of this applet was inspired by a [url=http://www.gogeometry.com/school-college/p860-triangle-three-medians-area.htm]post[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br][b]Feel free to move the vertices of the triangle anywhere at any time.[/b][br][b][color=#ff00ff]You can also control the measure of the pink angle using the pink slider.[/color][/b] [br][br]How many parallelograms exist here? [br][br]Why are these quadrilaterals parallelograms? [br][br][b][color=#0000ff]How can we formally prove what is dynamically illustrated here? [/color][/b][br]
Quick (Silent) Demo

Information: GoGeometry Action 97!