The Cyclic quadrilateral reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

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 π.
• 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 side lengths.

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