I think the explanation is very good in wikipedia, don't need any more than that. It should be very understandable.
1 Answers · Science & Mathematics · 24/05/2011
... parallel to AF. Likewise, the triangles AEC and AEM have the same area, because they have the same base (... applet should make the idea very clear. http://www.cut-the-knot. org /pythagoras/morey.shtml
4 Answers · Science & Mathematics · 28/04/2008