Reflection-induced perspectivities among triangles. (English) Zbl 1183.51014
Summary: In the plane of a reference triangle ABC, let DEF be a triangle and P a point. A line U through P is defined as a successful reflector through P if the reflection D\('\)E\('\)F\('\) of DEF in U is perspective to ABC, in the sense that the lines AD\('\), BE\('\), CF\('\) concur. The point of concurrence is the perspector, P(DEF,P,U).
The main theorem is that for given DEF and P, there are either infinitely many successful reflectors through P, or else there are at most four. Examples include choices of DEF and P for which the Steiner axes are the successful reflectors, and also choices for which there are infinitely many successful reflectors, in which case P is called a pivot for DEF. In three of the examples, the locus of P(DEF,P,U) as U rotates about P, called the pivotal curve, is the isogonal conjugate of a circle.
The main theorem is that for given DEF and P, there are either infinitely many successful reflectors through P, or else there are at most four. Examples include choices of DEF and P for which the Steiner axes are the successful reflectors, and also choices for which there are infinitely many successful reflectors, in which case P is called a pivot for DEF. In three of the examples, the locus of P(DEF,P,U) as U rotates about P, called the pivotal curve, is the isogonal conjugate of a circle.
MSC:
51N20 | Euclidean analytic geometry |
14H50 | Plane and space curves |
15A15 | Determinants, permanents, traces, other special matrix functions |