Chapter 7 - Applications of Trigonometry and Vectors - Section 7.4 Vectors, Operations, and the Dot Product - 7.4 Exercises - Page 329: 17

From the results of Exercise 13 and Exercise 14, we can see that $a+(b+c) = (a+b)+c$. Therefore, it appears that vector addition is associative.

In Exercise 13, we sketched the vector $a+(b+c)$. In Exercise 14, we sketched the vector $(a+b)+c$. From the results of Exercise 13 and Exercise 14, we can see that $a+(b+c) = (a+b)+c$. Therefore, it appears that vector addition is associative.