Art of Problem Solving
During AMC 10A/12A testing, the AoPS Wiki is in read-only mode and no edits can be made.

Ptolemy's Theorem: Difference between revisions

Dschafer (talk | contribs)
Created page
Definition: added links to other topics
Line 3: Line 3:
=== Definition ===
=== Definition ===


Given a cyclic quadrilateral <math>ABCD</math> with side lengths <math>{a},{b},{c},{d}</math> and diagonals <math>{e},{f}</math>:
Given a [[cyclic quadrilateral]] <math>ABCD</math> with side lengths <math>{a},{b},{c},{d}</math> and [[diagonals]] <math>{e},{f}</math>:


<math>ac+bd=ef</math>
<math>ac+bd=ef</math>

Revision as of 13:08, 18 June 2006

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 ${e},{f}$:

$ac+bd=ef$