## Pappus's Hexagon Theorem

If , , and are three points on one Line, , , and are three points on another Line, and meets at , meets at , and meets at , then the three points , , and are Collinear. Pappus's hexagon theorem dual to Desargues' Theorem according to the Duality Principle of Projective Geometry.

See also Cayley-Bacharach Theorem, Desargues' Theorem, Duality Principle, Pascal's Theorem, Projective Geometry

References

Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 73-74, 1967.

Ogilvy, C. S. Excursions in Geometry. New York: Dover, pp. 92-94, 1990.

Pappas, T. Pappus' Theorem & the Nine Coin Puzzle.'' The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, p. 163, 1989.