# Exeter point

In geometry, the Exeter point is a special point associated with a plane triangle. The Exeter point is a triangle center and is designated as the center X(22)[1] in Clark Kimberling's Encyclopedia of Triangle Centers. This was discovered in a computers-in-mathematics workshop at Phillips Exeter Academy in 1986.[2] This is one of the recent triangle centers, having been discovered only in 1986, unlike the classical triangle centers like centroid, incenter, and Steiner point.[3]

## Definition

The Exeter point is defined as follows.[2][4]

Let ABC be any given triangle. Let the medians through the vertices A, B, C meet the circumcircle of triangle ABC at A' , B' and C' respectively. Let DEF be the triangle formed by the tangents at A, B, and C to the circumcircle of triangle ABC. (Let D be the vertex opposite to the side formed by the tangent at the vertex A, E be the vertex opposite to the side formed by the tangent at the vertex B, and F be the vertex opposite to the side formed by the tangent at the vertex C.) The lines through DA' , EB' and FC' are concurrent. The point of concurrence is the Exeter point of triangle ABC.

## Trilinear coordinates

The trilinear coordinates of the Exeter point are

( a ( b4 + c4a4 ), b ( c4 + a4b4 ), c ( a4 + b4c4 ) ).

## References

1. ^ Kimberling, Clark. "Encyclopedia of Triangle Centers: X(22)". Retrieved 24 May 2012.
2. ^ a b Kimberling, Clark. "Exeter Point". Retrieved 24 May 2012.
3. ^ Kimberling, Clark. "Triangle centers". Retrieved 24 May 2012.
4. ^ Weisstein, Eric W. "Exeter Point". From MathWorld--A Wolfram Web Resource. Retrieved 24 May 2012.