Main Page | See live article | Alphabetical index In geometry, a cyclic quadrilateral is a quadrilateral whose vertices are all lie on a single circle. The vertices are said to be concyclic. Opposite angles of a cyclic quadrilateral add up to . The area of a cyclic quadrilateral is given by Brahmagupta's formula. The area of a cyclic quadrilateral is maximal among all quadrilaterals having the same (multi)set of side lengths. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.