Answer
Because the distance from Av to b is smaller than the distance from Au to b, u cannot be the least-squares solution to the equation.
Work Step by Step
$Au=\begin{bmatrix}
11\\-11\\11
\end{bmatrix}$
$||Au-b||=\sqrt{40}$
$Av=\begin{bmatrix}
7\\-12\\7
\end{bmatrix}$
$||Av-b||=\sqrt{29}$
Because the distance from Av to b is smaller than the distance from Au to b, u cannot be the least-squares solution to the equation.
