### A good answer might be:

The diagram shows sliding up the vector **e** until its tail touches the head
of **d**.

The sum is the vector from the tail of **d** to the head of **e** .

# Vector Addition in 3D

The diagram shows 3D vectors **a** and **b** added to form **c**
(the 3D box is there to aid in visualizing the
three dimensions).
The head-to-tail rule works in 3D as well.

When two vectors are added in 3D,
the head-to-tail rule defines
a triangle oriented in 3D space.