Ptolemy's Theorem

Revision as of 14:02, 18 June 2006 by Dschafer (talk | contribs) (Created page)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

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 ${p},{q}$:

$ac+bd=pq$

Invalid username
Login to AoPS