Difference between revisions of "Ptolemy's Inequality"

Revision as of 20:27, 24 June 2006

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

Revision as of 14:39, 21 June 2006 (view source) Inscrutableroot (talk \| contribs) m (proofreading) ← Older edit		Revision as of 20:27, 24 June 2006 (view source) ComplexZeta (talk \| contribs) (No need for convexity here) Newer edit →
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−	Ptolemy's Inequality for a ~~convex~~ quadrilateral ABCD states that AB·CD + BC·DA ≥ AC·BD with ~~equality if~~ ABCD is a [[cyclic quadrilateral]].	+	Ptolemy's Inequality for a [[quadrilateral]] ABCD states that AB·CD + BC·DA ≥ AC·BD with [[equal]]ity [[iff]] ABCD is a [[cyclic quadrilateral]].

	[http://planetmath.org/encyclopedia/ProofOfPtolemysInequality.html A proof of Ptolemy's inequality.]		[http://planetmath.org/encyclopedia/ProofOfPtolemysInequality.html A proof of Ptolemy's inequality.]