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Circumcevian Triangle


CircumcevianTriangle

The circumcevian triangle DeltaA^'B^'C^' of a point P with respect to a triangle DeltaABC has vertices at the second intersections of the lines AP, BP, and CP with the circumcircle of DeltaABC, respectively (Kimberling 1998, p. 201). Configurations in which an intersection is undefined or the resulting triangle is degenerate are excluded.

The circumcevian triangle DeltaA^'B^'C^' with respect to the point P=alpha:beta:gamma has trilinear vertex matrix

 [-abetagamma (bgamma+cbeta)beta (bgamma+cbeta)gamma; (calpha+agamma)alpha -bgammaalpha (calpha+agamma)gamma; (abeta+balpha)alpha (abeta+balpha)beta -calphabeta]
(1)

and area

 Delta^'=((calphabeta+balphagamma+abetagamma)^3Delta)/(abcF),
(2)

where Delta is the area of DeltaABC and

 F=(beta^2+gamma^2+2betagammacosA)(alpha^2+gamma^2+2alphagammacosB)(alpha^2+beta^2+2alphabetacosC).
(3)

Circumcevian triangles for various choices of P are summarized in the table below.

Every triangle inscribed in the circumcircle of a reference triangle DeltaABC is congruent to exactly one circumcevian triangle of DeltaABC (Kimberling 2005).

The circumcevian triangle of P is similar to the pedal triangle of P (Kimberling 1998). When both triangles are defined and nondegenerate, their corresponding sides are parallel iff P lies on the M'Cay cubic. When the resulting homothecy has a finite homothetic center, that center lies on the Lemoine cubic (Gibert).


See also

Circum-Medial Triangle, Circum-Orthic Triangle, D-Triangle

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References

Gibert, B. "Lemoine Cubic." http://bernard-gibert.fr/Exemples/k009.html.Gibert, B. "McCay Cubic = Griffiths Cubic." http://bernard-gibert.fr/Exemples/k003.html.Kimberling, C. "Triangle Centers and Central Triangles." Congr. Numer. 129, 1-295, 1998.Kimberling, C. "Transfigured Triangle Geometry." Preprint. Mar. 5, 2005.

Referenced on Wolfram|Alpha

Circumcevian Triangle

Cite this as:

Weisstein, Eric W. "Circumcevian Triangle." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CircumcevianTriangle.html

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