In geometry, given a triangle ABC, there exist unique points Aô, Bô, and Cô on the sides BC, CA, AB respectively, such that:
This is point X<sub>369</sub> in Clark Kimberling's Encyclopedia of Triangle Centers. Uniqueness and a formula for the trilinear coordinates of X<sub>369</sub> were shown by Peter Yff late in the twentieth century. The formula involves the unique real root of a cubic equation.