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Ptolemy's Inequality

Revision as of 20:27, 24 June 2006 by ComplexZeta (talk | contribs) (No need for convexity here)

Ptolemy's Inequality for a quadrilateral ABCD states that AB·CD + BC·DA ≥ AC·BD with equality iff ABCD is a cyclic quadrilateral.

A proof of Ptolemy's inequality.

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