ABC is an equilateral triangle. D andD′ are points on opposite sides of the plane ABC such that the two tetrahedra ABCD and ABCD′ are congruent (but not necessarily with the vertices in that order). If the polyhedron with the five vertices A,B,C,D,D′ is such that the angle between any two adjacent faces is the same, find DD′/AB . ratiogeometrytetrahedron3D geometry