Ptolemy's Theorem

Revision as of 14:08, 18 June 2006 by Rrusczyk (talk | contribs) (Definition: added links to other topics)

Ptolemy's theorem gives a relationship between the side lengths and the diagonals of a cyclic quadrilateral; it is the equality case of the Ptolemy inequality.

Definition

Given a cyclic quadrilateral $ABCD$ with side lengths ${a},{b},{c},{d}$ and diagonals ${e},{f}$:

$ac+bd=ef$

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