What relationship is dynamically being illustrated in the applet below? How can this relationship formally be proven true?
For more information, see this [url=http://www.gogeometry.com/problem/p762-parallelogram-midpoint-perpendicular-congruence-plane-geometry.htm]post[/url] from Antonio Gutierrez ([url=http://www.gogeometry.com/]GoGeometry[/url]).