The Circles on the Diagonals of a Complete Quadrilateral as Diameters are Coaxal. Furthermore, the Orthocenters of the four Triangles of a Complete Quadrilateral are Collinear on the Radical Axis of the Coaxal Circles.

**References**

Johnson, R. A. *Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle.* Boston, MA:
Houghton Mifflin, p. 172, 1929.

© 1996-9

1999-05-25