On Yiu's Equilateral Triangles Associated with a Kiepert Hyperbola

Abstract

In 2014, Paul Yiu constructed two equilateral triangles inscribed in a Kiepert hyperbola associated with a reference triangle. It was asserted that each of the equilateral triangles is triply perspective to the reference triangle, and in each case, the corresponding three perspectors are collinear. In this note, we give a proof of his assertions. Furthermore as an analogue of Lemoine's problem, we formulated and answered the question about how to recover the reference triangle given a Kiepert hyperbola, one of the two Fermat points and one vertex of the reference triangle.