# .

In geometry, the de Longchamps point of a triangle is the reflection of its orthocenter about its circumcenter.[1] It is listed as X(20) in the Encyclopedia of Triangle Centers. Its trilinear coordinates are

$$\displaystyle\cos A - \cos B \cos C : \cos B - \cos C \cos A : \cos C - \cos A \cos B$$

The orthocenter H reflected about the circumcenter O gives the de Longchamps point L.

The point is collinear with the orthocenter and circumcenter.[1]