Difference between revisions of "Ptolemy's Inequality"

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Ptolemy's inequality for a convex quadrilateral ABCD states that AB·CD + BC·DA ≥ AC·BD with equality iff ABCD is a [[cyclic quadrilateral]].
 
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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[http://planetmath.org/encyclopedia/ProofOfPtolemysInequality.html A proof of Ptolemy's inequality.]

Revision as of 13:16, 21 June 2006

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

A proof of Ptolemy's inequality.