QL-L2: Steiner Line

The Orthocenters of the 4 component triangles of a Quadrilateral are collinear. The line through these 4 Orthocenters is the Steiner Line.
The Steiner Line is also known as Ortholine.
QL-L2 is also called the Aubert Line. See Ref-72, Euclid-messages #2420, #2435 and Ref-66, QPG-messages #1149-1151.
QL-L2 is also called the “orthocentric line” by J.W. Clawson in Ref-31.
Jean-Louis Ayme wrote Ref-2a about the Newton Line as well as the Steiner Line.
QL-L2-Steiner Line-00

1st CT-coefficient:
            SA l (m - n)
1st DT-coefficient:
            b2 (l2-m2) - c2 (l2-n2)

  • QL-P2 (Morley Point) and QL-2P1a/b (1st/2nd Plücker Point) and QL-P7 (Newton-Steiner Point) and QL-P9 (Circumcenter QL-Diagonal Triangle) lie on QL-L2.
  • QL-L2 is parallel to QL-L3 (QL-Pedal Line).
  • QL-L2 is perpendicular to QL-L1 (Newton Line) and QL-L4 (Morley Line).
  • QL-L2 is the directrix of QL-Co1, the Inscribed Quadrilateral Parabola.
  • QL-L2 is the common radical axis of the three circles constructed on the diagonals of the Reference Quadrilateral as diameters. This is also known as the Gauss-Bodenmiller Theorem (see Ref-13).
  • QL-L2 is the Clawson-Schmidt Conjugate (QL-Tf1) of QL-Ci3 (Miquel Circle).
  • The Orthopole of a sideline of the complete quadrilateral with respect to the triangle bounded by the three other sidelines lies on the Steiner line (see Ref-4, page 42). The Orthopole of a line L wrt a Triangle = the common intersection point of the three lines perpendicular to the sidelines of the triangle, each passing through the projection of the opposite vertex on line L.
  • The Orthopoles of QL-L3 (pedal Line) wrt the QL-Component Triangles lie on QL-L2. See Ref-34, Seiichi Kirikami, QFG message # 1102.
  • The reflections of QL-P1 in the 4 basic lines of the Reference Quadrilateral lie on QL-L2. See Ref-34, Seiichi Kirikami, QFG message # 1091.
  • The reflections of QL-L2 in the 4 basic lines of the Reference Quadrilateral concur in QL-P1. See Ref-34, Seiichi Kirikami, QFG message # 1095.
  • QL-L2 is the common Steiner Line (in a triangle) of QL-P1 wrt the 4 QL-Component Triangles (Def.: The reflections of a point P of the circumcircle on the sides of the triangle lie on a line called the Steiner line of P wrt that triangle). See Ref-34, QFG #1105.


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