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Synthetic foundations of cevian geometry. II: The center of the cevian conic. (English) Zbl 1372.51014

Following [J. Geom. 108, No. 1, 45–60 (2017; Zbl 1370.51019)], the authors proceed in their investigation of a triangle \(ABC\), a point \(P\) in general position and its isotomcomplement \(Q\) (the complement of the isotomic conjugate \(P'\) of \(P\)). The focus of this article is on the conic \(C_P\) through \(A\), \(B\), \(C\), \(P\), and \(Q\).
This conic also contains the isotomic conjugate \(P'\), its isotomcomplement \(Q'\), and a couple of points derived from these points. If \(T_P\) denotes the affine map that maps \(ABC\) to the Cevian triangle of \(P\), the maps \(T_P\) and \(T_{P'}\) are conjugate in the affine group and the affine map \(\lambda := T_{P'} \circ T_P^{-1}\) fixes \(C_P\). Its unique ordinary fixed point is the center of \(C_P\) and it allows an interpretation as transformation in the Cayley-Klein model of hyperbolic geometry defined by \(C_P\).
These results (and quite a few more) are proved by synthetic reasoning alone. A forthcoming third part deals with the interpretation of the center \(Z\) of the Cevian conic \(C_p\) as generalized Feuerbach point.
For Part I, see [the authors, J. Geom. 108, No. 1, 45–60 (2017; Zbl 1370.51019)], for Part III, see [the authors, ibid. 108, No. 2, 437-455 (2017; doi:10.1007/s00022-016-0350-2)].

MSC:

51M15 Geometric constructions in real or complex geometry
51A05 General theory of linear incidence geometry and projective geometries
51A20 Configuration theorems in linear incidence geometry
51M09 Elementary problems in hyperbolic and elliptic geometries
51N10 Affine analytic geometry

Citations:

Zbl 1370.51019