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

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

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.

Is it possible (do you think) to add three vectors together,
like **a**+**b**+**d** in the figure?