KnowraPtolemy's theoremLinked fromLinked fromThe 16 pages that link to Ptolemy's theorem, each with the reason it gives.All 16Related 9Compared with 7Cyclic quadrilateralRelated: It links all four side lengths to both diagonals when the vertices are concyclic.Brahmagupta's formulaRelated: Its relation among sides and diagonals helps derive the area formula.Bretschneider's formulaRelated: It offers another route from cyclic geometry to Brahmagupta's area result.Tangent–secant theoremRelated: Both results turn cyclic geometry into length equations, though Ptolemy’s theorem concerns quadrilaterals.Stewart's theoremRelated: Like Stewart’s theorem, it converts a geometric configuration into an exact length identity.Inversive geometryRelated: Inversion can establish this relation by sending a vertex to infinity and simplifying the cyclic figure.Casey's theoremRelated: Casey's relation replaces vertex distances with common-tangent lengths.Haruki's theoremRelated: Cyclic quadrilaterals can turn circle intersections into tractable segment equations.Van Schooten's theoremRelated: Both results convert cyclic point configurations into exact equations among segment lengths.