ABCD is a parallelogram,
and![]()
Because vectors can be moved and
is parallel to, and the same length as
we can write![]()
Similarly, since
is parallel to, and the same length as
so we can write![]()

Vectors add in a natural way so
and![]()
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 is
and from C to M is
is since
is against the direction of![]()
![]()
Parallel Vectors
Any vector that is a multiple of
is parallel to
so
is parallel to![]()