How Unusual Is This Viewer?

A streaming service turns every viewer into a vector. Each viewer's average star rating in three genres becomes one coordinate, so a viewer is a point in a three-dimensional "taste space". Here are this week's four viewers:

Viewer	Action	Comedy	Drama
A	$8$	$3$	$5$
B	$2$	$9$	$4$
C	$6$	$5$	$9$
D	$4$	$7$	$6$

Before the recommender compares anybody, it mean-centres the data. It builds the average viewer

$\bar{v} = \tfrac{1}{4}\left(\vec{v}_A + \vec{v}_B + \vec{v}_C + \vec{v}_D\right)$

and replaces each viewer by their taste vector

$\vec{t} = \vec{v} - \bar{v}$

which records not what someone rated, but how far they sit from the crowd.

How unusual is viewer A? That is, what is the length $\lVert \vec{t}_A \rVert$ of viewer A's taste vector?

Round your answer to two decimal places.

How Unusual Is This Viewer?

Hints