Answer
$\sqrt{3}$
Work Step by Step
Let us consider that vector $v$ is given by:
$v=pi+qj+rz$
The magnitude of a vector can be determined using the formula
$||v||=\sqrt{p^2+q^2+r^2} ...(1)$
We will use the formula (1) to obtain:
$||v||=\sqrt{(-1)^2+(-1)^2+(1)^2}\\
=\sqrt{1+1+1}\\
=\sqrt{3}$