PreprintCC BY-NC-ND 4.0arXiv
Euclidean Triangles Associated with Diophantine D(4)-triples
Abstract
In this paper we study Euclidean triangles associated with Diophantine D(4)-triples. For a D(4)-triple {a,b,c}, a<b<c, we prove that the lengths r=√(ab+4), s=√(ac+4) and t=√(bc+4) associated with this D(4)-triple form a non-degenerate triangle if and only if the triple is regular and r>b−a. For a fixed shortest side r, we describe all triangles associated with D(4)-triples in terms of the factorisations of r2−4, give a divisor criterion for their number, and determine their angle type. We also prove that two similar triangles associated with D(4)-triples are necessarily congruent. Finally, for the family of D(4)-triples {r−2,r+2,4r}, we obtain a Pell-equation characterisation of the Heronian triangles associated with these D(4)-triples.
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BibTeX
@misc{trebjesanin2026euclidean,
title = {{Euclidean Triangles Associated with Diophantine $D(4)$-triples}},
author = {Marija Bliznac Trebješanin and Jelena Pleština},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.38544},
eprint = {2609.38544},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.38544},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Euclidean Triangles Associated with Diophantine D(4)-triples
AU - Marija Bliznac Trebješanin
AU - Jelena Pleština
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.38544
UR - https://arxiv.org/abs/2609.38544
AB - In this paper we study Euclidean triangles associated with Diophantine D(4)-triples. For a D(4)-triple {a,b,c}, a<b<c, we prove that the lengths r=√(ab+4), s=√(ac+4) and t=√(bc+4) associated with this D(4)-triple form a non-degenerate triangle if and only if the triple is regular and r>b−a. For a fixed shortest side r, we describe all triangles associated with D(4)-triples in terms of the factorisations of r^2−4, give a divisor criterion for their number, and determine their angle type. We also prove that two similar triangles associated with D(4)-triples are necessarily congruent. Finally, for the family of D(4)-triples {r−2,r+2,4r}, we obtain a Pell-equation characterisation of the Heronian triangles associated with these D(4)-triples.
ER -