Answer
$8$
Work Step by Step
Let us consider that a 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} $
Here, we have:
$||-4 v||=|-4| ||v|| =(4)(2)=8$
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