Chapter 7 - Applications of Trigonometry and Vectors - Section 7.4 Vectors, Operations, and the Dot Product - 7.4 Exercises - Page 332: 13

We can first use the vector $b$ and the vector $c$ to sketch the vector $b+c$. Then we can use the vector $a$ and the vector $b+c$ to make a parallelogram. The resultant vector through the middle of the parallelogram is the vector $a+(b+c)$.

To sketch the vector $a+(b+c)$, we can first use the vector $b$ and the vector $c$ to sketch the vector $b+c$. Then we can use the vector $a$ and the vector $b+c$ so that their initial points coincide. Then we can use another copy of the vector $a$ and the vector $b+c$ to complete the parallelogram. The resultant vector through the middle of the parallelogram is the vector $a+(b+c)$.