Ptolemy's Inequality

Revision as of 15:52, 20 June 2006 by Cosinator (talk | contribs) (A link to 'cyclic quadrilateral' in case someone doesn't know what it is.)

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

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