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McCay cubic

Plane curve unique to a given triangle From Wikipedia, the free encyclopedia

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In Euclidean geometry, the McCay cubic (also called M'Cay cubic[1] or Griffiths cubic[2]) is a cubic plane curve in the plane of a reference triangle and associated with it. It is the third cubic curve in Bernard Gilbert's Catalogue of Triangle Cubics and it is assigned the identification number K003.[2]

Definition

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  Reference triangle ABC
  Nine-point circle of ABC
  Pedal triangle of point P
  Pedal circle (circumcircle of pedal triangle) of P
  McCay cubic: locus of P such that the pedal circle and nine point circle are tangent

The McCay cubic can be defined by locus properties in several ways.[2] For example, the McCay cubic is the locus of a point P such that the pedal circle of P is tangent to the nine-point circle of the reference triangle ABC.[3] The McCay cubic can also be defined as the locus of point P such that the circumcevian triangle of P and ABC are orthologic.

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Equation of the McCay cubic

The equation of the McCay cubic in barycentric coordinates is

The equation in trilinear coordinates is

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McCay cubic as a stelloid

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McCay cubic with its three concurring asymptotes

A stelloid is a cubic that has three real concurring asymptotes making 60° angles with one another. McCay cubic is a stelloid in which the three asymptotes concur at the centroid of triangle ABC.[2] A circum-stelloid having the same asymptotic directions as those of McCay cubic and concurring at a certain (finite) is called McCay stelloid. The point where the asymptoptes concur is called the "radial center" of the stelloid.[4] Given a finite point X there is one and only one McCay stelloid with X as the radial center.

References

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