Cyclic quadrilateral

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.