Dot Product - Question

Let

u = [\begin{matrix} 1 \\ - 2 \\ 1 \end{matrix}]

and let

v = [\begin{matrix} 3 \\ 1 \\ - 1 \end{matrix}]

The answer is 0.

$\begin{array}{rcl} u \cdot v & = & u_{1} v_{1} + u_{2} v_{2} + u_{3} v_{3} \\ = & (1) (3) + (- 2) (1) + (1) (- 1) \\ = & 3 - 2 - 1 \\ = & 0. \end{array}$