The areas of two opposite quadrilaterals

Author:
Idan Tal

The areas of two opposite quadrilaterals

The applet illustrate the property according to which thesum of the opposite quadrilaterals always equals half the area of the quadrilateral ABCD, we construct a GeoGebra applet in which one can drag each of the vertices of the quadrilateral ABCD, and for each location of the vertices (including a concave quadrilateral), the screen shows the sum of the areas of the opposite quadrilaterals.