For a Quadrilateral with sides of length , , , and , the Area is given by

(1) |

(2) |

(3) | |||

(4) |

where is the Radius of the Circumcircle. If the Quadrilateral is Inscribed in one Circle and Circumscribed on another, then the Area Formula simplifies to

(5) |

**References**

Coxeter, H. S. M. and Greitzer, S. L. *Geometry Revisited.* Washington, DC: Math. Assoc. Amer., pp. 56-60,
1967.

Johnson, R. A. *Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle.* Boston, MA:
Houghton Mifflin, pp. 81-82, 1929.

© 1996-9

1999-05-26