Find the angle between the diagonals of the back and left faces of a cube with one vertex on the origin.
A) 60 degrees
B) arcos(1/sqrt(6))
C) arcos(1/(3sqrt(2))
D) 90 degrees
E) 120 degrees.
I think the answer should be D) 90 degrees. Since these vectors are diagonals on the face of the cube...