Prove that the x-coordinate of the fifth apex of a regular hexahedron is
X5 = (2/3)(x4 + x3 + x2) – x1
In this case, the hexahedron is made from two tetrahedrons joined at on face, and the first four x-coordinates are x1, x2, x3, and x4. X2, x3, x4 are the ponts closest to x5.
A friend of mine gave me this formula. I have looked at his proof, and I think it only works for a figures with a figure with edges of magnitude equal to 2.
The more general formula would probably have different coeficients.