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Equal Parallelians Point


EqualParalleliansPoint

Through a point K in the plane of a triangle DeltaABC, draw parallelians through a point as illustrated above. Then there exist four points K for which P_(AC)P_(CA)=P_(AB)P_(BA)=P_(BC)P_(CB), i.e., for which the segments of the parallels have equal length.

To restrict these four points, let the length of P_(BC)P_(CB) be considered negative if P_(BC) lies on the extension of AB beyond A and P_(CB) lies on the extension of CA beyond A, and positive otherwise. Define the lengths of the other two parallelians to be signed in the analogous manner. With this sign convention, there is a unique point K for which the signed parallelians have equal length. This point is called the equal parallelians point of DeltaABC.

It has equivalent triangle center functions

alpha_(192)=bc(ca+ab-bc)
(1)
alpha_(192)=1/a(-1/a+1/b+1/c)
(2)

and is Kimberling center X_(192) (Kimberling 1998, p. 104).

The length L of the equal parallelians is

L=2/(a^(-1)+b^(-1)+c^(-1))
(3)
=(2abc)/(bc+ca+ab).
(4)
EqualParalleliansEllipse

As is true for general parallelians, those for the X_(192) lie on an ellipse. The center of this ellipse has triangle center function

 alpha=((ab+ac-bc)(3a^2b^2-2a^2bc-6ab^2c+3a^2c^2-4abc^2+b^2c^2))/a,
(5)

which is not a Kimberling center.

EqualParalleliansIncenter

The equal parallelians point is also the perspector of the incentral triangle DeltaA_IB_IC_I and anticomplementary triangle DeltaA^'B^'C^' of DeltaABC (Kimberling 1998, p. 105).


See also

Congruent Isoscelizers Point, Parallelian

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References

Bier, S. "Equilateral Triangles Intercepted by Oriented Parallelians." Forum Geom. 1, 25-32, 2001. http://forumgeom.fau.edu/FG2001volume1/FG200105index.html.Kimberling, C. "Triangle Centers and Central Triangles." Congr. Numer. 129, 1-295, 1998.Kimberling, C. "Equal Parallelians Point." http://faculty.evansville.edu/ck6/tcenters/recent/eqparal.html.Kimberling, C. "Encyclopedia of Triangle Centers: X(192)=X(1)-Ceva Conjugate of X(2) (Equal Parallelians Point)." http://faculty.evansville.edu/ck6/encyclopedia/ETC.html#X192.Yiu, P. "Geometric Constructions VII: Solution of GC15." Math. and Informatics Quart. http://www.math.fau.edu/yiu/MIQGeomConstructions7.ps.

Referenced on Wolfram|Alpha

Equal Parallelians Point

Cite this as:

Weisstein, Eric W. "Equal Parallelians Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/EqualParalleliansPoint.html

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