# Brianchon theorem

If an hexagon $ABCDEF$ (not necessarily convex) is inscribed into a conic (in particular into a circle), then the three diagonals $AD,BE,CF$ are concurrent. This theorem is the dual of Pascal line theorem. (C. Brianchon, 1806)

Proof:It follows by duality.

Title Brianchon theorem BrianchonTheorem 2013-03-22 14:04:29 2013-03-22 14:04:29 vmoraru (1243) vmoraru (1243) 7 vmoraru (1243) Theorem msc 51-00