<s>[INST] Matrix vector form. Is this in the correct form? I have this question:

Write the linear system
  $$\begin{array}{rcr}-2x_1+x_2-4x_3 & = & 1 \\ x_1-2x_2 & = & -3 \\ x_1+x_2-4x_3 & = & 0 \end{array}$$
  in the matrix-vector form $A\mathbf{x}=\mathbf{b}$.

Is this what they want?
$$ 
x_1*
\begin{bmatrix}
  -2 \\ 1 \\ 1
\end{bmatrix}
+
x_2*
\begin{bmatrix}
  1 \\ -2 \\ 1
\end{bmatrix}
+
x_3*
\begin{bmatrix}
  -4 \\ 0 \\ -4
\end{bmatrix}
=
\begin{bmatrix}
  1 \\ -3 \\ 0
\end{bmatrix}
$$
 [/INST] basically! 
$
A = \begin{pmatrix} -2 & 1 & -4 \\ 1 & -2 & 0 \\ 1 & 1 & -4 \end{pmatrix}
$
and $b = \begin{pmatrix} 1 \\ -3 \\ 0 \end{pmatrix}$ yielding $Ax = b$. 
</s>