A good answer might be:

The displacement from point B to point A is:

So the column matrix representing the displacement is:

e = (-5, -2)T


When the points are visited in the opposite order, the displacement vector points in the opposite direction. In the column matrix each element is -1 times the old value.

The displacement from A to B is different from the displacement from B to A. Think of displacement as "directions on how to walk from one point to another." So, if you are standing on point A and wish to get to point B, the displacement (3, 1)T says "walk 3 units in the positive X direction, then walk 1 unit in the positive Y direction."

Of course, to get from point B to point A you need different directions: the displacement (-3, -1)T says "walk 3 units in the negative X direction, then walk 1 unit in the negative Y direction," which puts you back on point A.

The displacement from point Start to point Finish ==

(Finish x - Start x , Finish y - Start y)T


Say that point C is   x=4, y=2   and that point D is   x=3, y= 5 .  What column matrix represents the displacement from C to D?