Four faces of tetrahedron ABCD are congruent triangles whose angles form an arithmetic progression. If the lengths of the sides of the triangles are a<b<c, determine the radius of the sphere circumscribed about the tetrahedron as a function on a,b, and c. What is the ratio c/a if R=a ? ratiogeometry3D geometrytetrahedronspherefunctioncongruent triangles