English

Rational angle bisectors on the coordinate plane and solutions of Pell's equations

Number Theory 2025-01-03 v9

Abstract

On the coordinate plane, the slopes aa and bb of two straight lines and the slope cc of one of their angle bisectors satisfy the equation (ac)2(b2+1)=(bc)2(a2+1).(a-c)^2(b^2+1) = (b-c)^2(a^2+1). Recently, an explicit formula for nontrivial integral solutions of this equation with solutions of negative Pell's equations was discovered by the author. In this article, for a given square-free integer d>1d > 1 and a given integer z>1,z > 1, we describe every integral solution (x,y)(x,y) of x2dy2=z|x^2-dy^2| = z such that xx and dydy are coprime by using the fundamental unit of Q(d)\mathbb Q(\sqrt d) and elements of Z[d]\mathbb Z[\sqrt d] whose absolute value of norms are the smallest prime powers. We also describe every nontrivial rational solution of the above equation as one of its applications.

Keywords

Cite

@article{arxiv.2305.01091,
  title  = {Rational angle bisectors on the coordinate plane and solutions of Pell's equations},
  author = {Takashi Hirotsu},
  journal= {arXiv preprint arXiv:2305.01091},
  year   = {2025}
}

Comments

14 pages, 3 figures; Corrected misprints; Revised Definition 1 (2), Theorem 3, and its proof, and changed the numbering of theorems after the seventeenth version