Hyperbolic Heron triangles and elliptic curves

Abstract

We define hyperbolic Heron triangles (hyperbolic triangles with “rational” side-lengths and area) and parametrize them in two ways via rational points of certain elliptic curves. We show that there are infinitely many hyperbolic Heron triangles with one angle α and area A for any (admissible) choice of α and A; in particular, the congruent number problem has always infinitely many solutions in the hyperbolic setting. We also explore the question of hyperbolic triangles with a rational median and a rational area bisector (median splitting the triangle in half).