# On the volume of a hyperbolic tetrahedron

##
Nikolay Abrosimov

created by collari on 17 Oct 2024

modified on 18 Oct 2024

12 nov 2024
-- 14:30

Aula Magna, Dipartimento Matematica, Pisa

**Abstract.**

The talk will give an overview of the latest results on finding exact formulas for calculating the volumes of hyperbolic tetrahedra. The classical formula of G. Sforza expresses the volume of a hyperbolic tetrahedron of a general form in terms of dihedral angles. Its modern proof is proposed in. The formula in terms of edge lengths is obtained in the recent joint work of the author with B. Vuong. The known formulas for the volume of a hyperbolic tetrahedron of a general form are very complicated and cannot always be applied to calculate the volumes of more complex polyhedra. So, natural question arises to find more convenient and simple formulas for sufficiently wide families of hyperbolic tetrahedra. At the end of the talk we will consider hyperbolic tetrahedra of special types: ideal, biorthogonal, 3-orthogonal and their generalizations. The volume of the ideal and biorthogonal tetrahedron was known to N.I. Lobachevsky. We will present new formulas for calculating volumes and normalized volumes of a trirectangular hyperbolic tetrahedron as well as its generalization for 4-parameter family of tetrahedra with one edge orthogonal to the face. The latter formulas can be used to calculate the volumes of more complex polyhedra in the Lobachevsky space.