Ptolemy's Theorem

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Let ABCD be a quadrilateral where all the vertices lie on a circle. As long as the (green) diagonals cross, ; in words, the sum of the products of the two pairs of opposite sides equals the product of the diagonals.


Drag any vertex to another location on the circle.


Contributed by: Jay Warendorff (March 2011)
Open content licensed under CC BY-NC-SA




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