Chapter 7 - Applications of Trigonometry and Vectors - Section 7.4 Vectors, Operations, and the Dot Product - 7.4 Exercises - Page 332: 14

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