# Brahmagupta's Formula For The Area of Any Cyclic Quadrilateral *Brahmagupta's Formula* is a generalization of the [[Heron's Formula For The Area of Any Triangle|Heron’s Formula]] (a triangle can be thought of as a cyclic quadrilateral whose fourth side is 0). It is **used to calculate the area of a cyclic quadrilateral** [^1]. [^1]: A cyclic quadrilateral is a quadrilateral whose points all lie on a single [[circle]] i.e. one for which a circumcircle exists. Let $s$ be the semi-perimeter of the quadrilateral ($s=\frac{a+b+c+d}{2}$), then the quadrilateral's area $A$ is $ A=\sqrt{(s-a)(s-b)(s-c)(s-d)} $ A generalization of this formula is [[Bretschneider's Formula for The Area of Any Quadrilateral]].