GoGeometry Action 180!

Creation of this resource was inspired by this [url=http://www.gogeometry.com/school-college/3/p1283-equilateral-triangle-midpoint-perperpendicular.htm]problem[/url] posted by [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]You can move any of the [b]LARGE POINTS[/b] anywhere you'd like [b]AT ANY TIME[/b]. [br]As you do, notice that the diagonals of this quadrilateral always remain perpendicular. [br][br][color=#ff00ff][b]How can we formally prove what is dynamically illustrated here? [/b][/color]
Quick (Silent) Demo

Information: GoGeometry Action 180!