ABCD is a parallelogram,and
Because vectors can be moved andis parallel to, and the same length aswe can write
Similarly, sinceis parallel to, and the same length asso we can write
Vectors add in a natural way soand
Suppose now that we find the midpoint of AC and call it M and we find the midpoint of BC and call it N. Because M and N are the midpoints of AC and BC respectively,and
Suppose we want to find the vector vec NM.
We can go from N to C and then from C to M. From N to C isand from C to M isis sinceis against the direction of
Any vector that is a multiple ofis parallel tosois parallel to