Interactive Applet |
You can move the points A, B and C (click on the point and drag it).
Press the keys “+” and “−” to zoom in or zoom out the visualization window and use the arrow keys to translate it.
You can also construct all centers related with this one (as described in ETC) using the “Run Macro Tool”. To do this, click on the icon _{}, select the center name from the list and, then, click on the vertices A, B and C successively.
Information from Kimberling's Encyclopedia of Triangle Centers |
Trilinears f(A,B,C) : f(B,C,A) : f(C,A,B), where f(A,B,C) = sec A + 2 cos(B - C)
= g(A,B,C) : g(B,C,A) : g(C,A,B), where g(A,B,C) = cos(2B-C) cos(A-C) + cos(2C-B) cos(A-B)
Barycentrics (sin A)f(A,B,C) : (sin B)f(B,C,A) : (sin C)f(C,A,B)Traian Lalescu (Trajan Lalesco) proved in "A Class of Remarcable Triangles," Gazeta Matematica 20 (1915) 213 [in Romanian], that if triangles DEF and D'E'F' are inscribed in a circle and directed arclengths satisfy
arc DD' + arc EE' + arc FF' = 0 mod 2π, then the Simson lines of D,E,F with respect to D',E',F' and the Simson lines of D',E',F' with respect to D,E,F concur in the midpoint X of the segment of the orthocenters of DEF and D'E'F'. Daniel Vacaretu considered triangles DEF and D'E'F' associated with left and right isoscelizers and inscribed in the sine-triple-angle circle. He obtained the second set of trilinears shown above for the midpoint X. (See also the bicentric pair PU(61).)In Episodes in Nineteenth and Twentieth Century Euclidean Geometry,, page 132, Ross Honsberger presents X(1594) as the orthopole of the six sides of two triangles and as the point common to six Simson lines. Honsberger calls this orthopole the Rigby Point. (Notes on Lalescu and Honsberger received from D. Vacaretu, 19/16/03)
X(1594) lies on these lines:
2,3 6,70 50,252 53,566 67,1173 96,275 125,389 128,136 232,1508 264,847 325,1235 933,1166 1209,1216 1225,1238X(1594) = inverse-in-nine-point-circle of X(186)
X(1594) = inverse-in-orthocentroidal-circle of X(24)
X(1594) = X(933)-Ceva conjugate of X(523)
X(1594) = crosspoint of X(I) and X(J) for these (I,J): (4,93), (264,275)
X(1594) = crosssum of X(I) and X(J) for these (I,J): (3,49), (184,216)