Find the angle between the diagonal of the back and left faces of a cube with one vertex on the origin
A) 60 degrees
B) cos^-1(1/sqrt(6))
C) cos^-1(1/3*sqrt(2))
D) 90 degrees
E) 120 degrees
The two diagonals eminate from the vertex at the origin.
I will write [u] to mean the "norm"...