Brianchon's Theorem

The Dual of Pascal's Theorem. It states that, given a 6-sided Polygon Circumscribed on a Conic Section, the lines joining opposite Vertices (Diagonals) meet in a single point.

$\begin{figure}\begin{center}\BoxedEPSF{Branchions_Theorem.epsf}\end{center}\end{figure}$

References

Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 77-79, 1967.

Ogilvy, C. S. Excursions in Geometry. New York: Dover, p. 110, 1990.