A variable tetrahedron ABCD has the following properties:
Its edge lengths can change as well as its vertices, but the opposite edges remain equal (BC=DA,CA=DB,AB=DC); and the vertices A,B,C lie respectively on three fixed spheres with the same center P and radii 3,4,12. What is the maximal length of PD? geometry3D geometrytetrahedronspheregeometry unsolved