Wednesday, November 9, 2011

van Aubel's Theorem

Squares are placed outwardly at each side of quadrilateral ABCD. The center of the squares on the opposite sides are connected with segments (PN and MO). Move points A, B, C and D and observe what happens. Make a conjecture about your observations.

This is a Java Applet created using GeoGebra from - it looks like you don't have Java installed, please go to

Van Aubel's Theorem

Given an arbitrary planar quadrilateral, place a square outwardly on each side, and connect the centers of opposite squares. Then van Aubel's theorem states that the two lines are of equal length and cross at a right angle.

Click here to download GGB file.

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