If the co-ordinates of the points P and Q be (1, -2, 1) and (2, 3, 4) and O be the origin, then
If the co-ordinates of the points P,Q,R,S be (1, 2, 3), (4, 5, 7), (– 4, 3, – 6) and (2, 0, 2) respectively, then