Chapter 1 - Vectors - 1.2 Length and Angle: The Dot Product - Exercises 1.2 - Page 290: 3

$11$

For the matrices $u=\begin{bmatrix} u_{1} \\ u_{2} \\ \vdots\\ u_{n} \end{bmatrix}$ and $v=\begin{bmatrix} v_{1} \\ v_{2} \\ \vdots\\ v_{n} \end{bmatrix}$ The dot product is: $u\cdot v=u_1\cdot v_1+u_2\cdot v_2+...+u_n\cdot v_n.$ Hence, it follows: $u\cdot v=1\cdot 2+2\cdot 3+3\cdot 1=2+6+3=11.$