Poncelet Triangles: a Theory for Locus Ellipticity
This provides a theoretical framework for geometric analysis in triangle families, addressing a previously case-by-case problem, but it is incremental as it builds on existing Poncelet theory.
The paper tackles the problem of predicting whether the locus of a triangle center in certain Poncelet triangle families is a conic, specifically for confocal pairs and an outer ellipse with an inner concentric circular caustic, and shows that the locus' turning number is +/- 3 while predicting its monotonicity with respect to vertex motion.
We present a theory which predicts if the locus of a triangle center over certain Poncelet triangle families is a conic or not. We consider families interscribed in (i) the confocal pair and (ii) an outer ellipse and an inner concentric circular caustic. Previously, determining if a locus was a conic was done on a case-by-case basis. In the confocal case, we also derive conditions under which a locus degenerates to a segment or a circle. We show the locus' turning number is +/- 3, while predicting its monotonicity with respect to the motion of a vertex of the triangle family.