Vector Mid Point vs Mid Point Formula Given $OA=(2,9,-6)$ and $OB=(6,-3,-6)$. If $D$ is the midpoint, isit 
$OD=((2+6)/2, (9-3)/2, (-6-6)/2)$?
The correct answer is 
$OD=\frac{1}{2}AB=(2,-6,0)$

Your first answer is the midpoint of the line segment that joins the tip of the vector $OA$ to the tip of the vector $OB$.  The one that you call the correct answer is gotten by putting the vector $AB$ into standard position with, its initial end at the origin, and then finding the midpoint.
