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'Thebault's Theorem' printed from

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Take any parallelogram and draw squares on the sides of the parallelogram. What can you prove about the quadrilateral formed by joining the centres of these squares?

You can change the parallelogram by dragging the vertices.


This dynamic image is drawn using Geogebra, free software and very easy to use. You can download your own copy of Geogebra from together with a good help manual and Quickstart for beginners.