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Lester Circle


LestersCircle

The Lester circle is the circle on which the circumcenter C, nine-point center N, and the first and second Fermat points X and X^' lie (Kimberling 1998, pp. 229-230). Besides these (Kimberling centers X_3, X_5, X_(13), and X_(14), respective), no other notable triangle centers lie on the circle.

The Lester circle has circle function

 l=-(f(a,b,c)R^2[1+2cos(2A)])/(6a^2bc(a^2-b^2)(a^2-c^2)),
(1)

where

 f(a,b,c)=a^6-3a^4b^2+3a^2b^4-b^6-3a^4c^2-a^2b^2c^2+b^4c^2+3a^2c^4+b^2c^4-c^6
(2)

does not appear to have a simple form and l does not appear in Kimberling's list of triangle centers. The center of the Lester circle is

 alpha=bc(b^2-c^2)[2(a^2-b^2)(c^2-a^2)+3R^2(2a^2-b^2-c^2)-a^2(a^2+b^2+c^2)+a^4+b^4+c^4],
(3)

where R is the circumradius of the reference triangle, which is Kimberling center X_(1116). The radius of the Lester circle is given by

 R_L=(R^2sqrt(1-8cosAcosBcosC))/(6abc(a+b)(b+c)(c+a)|(a-b)(b-c)(c-a)|)sqrt(g(a,b,c)),
(4)

where g(a,b,c) is a symmetric 16th-order polynomial that does not appear to have a simple form.

LesterCircleOrthogonal

It is orthogonal to the orthocentroidal circle.


See also

Circumcenter, Fermat Points, Nine-Point Center

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References

Ahlschwede, T. "Lester's Circle Theorem." http://www.ops.org/north/curriculum/math/ahlsch/lester.htm.Kimberling, C. "Lester Circle." Math. Teacher 89, 26, 1996.Kimberling, C. "Triangle Centers and Central Triangles." Congr. Numer. 129, 1-295, 1998.Lester, J. "Triangles III: Complex Triangle Functions." Aequationes Math. 53, 4-35, 1997.Trott, M. "Applying GroebnerBasis to Three Problems in Geometry." Mathematica Educ. Res. 6, 15-28, 1997. http://library.wolfram.com/infocenter/Articles/1754/. Trott, M. "A Proof of Lester's Circle Theorem." http://library.wolfram.com/infocenter/Demos/124/.

Referenced on Wolfram|Alpha

Lester Circle

Cite this as:

Weisstein, Eric W. "Lester Circle." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LesterCircle.html

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