Polygons with equal area

1. Drag point B. What do you notice about the area of the polygon?
2. Drag point C. What polygons are formed? What can be said about its area?
3. Drag points C and D to form a pentagon.

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

What must be true about vertex A and vertex C that dragging them does not change the area of the polygons formed?

Erlina Ronda, http://math4teaching.com, Created with GeoGebra