Brianchon's Theorem

Theorem

Let tangents to $6$ points on a conic section $K$ form a hexagon $H$ to circumscribe the $K$.

Then the main diagonals of $H$ meet at a single point.

Proof

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Also see

• Pascal's Theorem

Source of Name

This entry was named for Charles Julien Brianchon.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $6$
• 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics ... (previous) ... (next): Entry: Brianchon's theorem
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $6$
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): Entry: Brianchon's theorem
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): Entry: Brianchon's theorem