This is true if one vector has the same direction as the other.

This situation is illustrated in the diagram.
The head-to-tail rule is used to sum two vectors pointing in the same direction.
(Vectors in the same direction are called **collinear**).
The sum vector is slightly moved out of its correct position so that
you can see it.
The summed vectors are **( 4, 3 ) ^{T}**
and

For now, to determine if two vectors have the same direction look at a picture or use geometry. Later on you will see a procedure to test if two vectors point in the same direction.

This example is a case where the "=" sign in the formula applies:

length(u+v) <= length(u) + length(v)

Can you think of *another* case in which the "=" sign applies?