  This paper will extend a known relationship between the circumradius and
dihedral angles of a tetrahedron in three-dimensional Euclidean space to
three-dimensional affine space over a general field not of characteristic two,
using only the framework of rational trigonometry devised by Wildberger. In
this framework, a linear algebraic view of trigonometry is presented, which
allows the associated three-dimensional vector space of such a
three-dimensional affine space to be equipped with a non-degenerate symmetric
bilinear form; this will also generalise the results presented to arbitrary
geometries parameterised by such a non-degenerate symmetric bilinear form.
