A fundamental property of the Fermat-Torricelli point for tetrahedra in the three dimensional Euclidean Space

We prove the following fundamental property for the Fermat-Torricelli point for four non-collinear and non-coplanar points forming a tetrahedron in ${\mathbb{R}}^3,$ which states that: The three bisecting lines having as a common vertex the Fermat-Torricelli point formed by each pair of equal angles, which are seen by the opposite edges of the tetrahedron meet perpendicularly at the Fermat-Torricelli point. Furthermore, we give an alternative proof, which is different from the one obtained by Bajaj and Mehlhos for the unsolvability of the Fermat-Torricelli problem for tetrahedra in ${\mathbb{R}}^3$ using only algebraic computations for some angles, which have as a common vertex the Fermat-Torricelli point of the tetrahedron.