4. Write down the augmented matrix for each of the linear systems in Exercise 3.
In each part of Exercises 5-6, find a linear system in the unknowns $x_1, x_2, x_3, \dots$, that corresponds to the given augmented matrix.
\begin{align*}
5. \text{ (a)} \begin{bmatrix} 2 & 0 & 0 \\ 3 & -4 & 0 \\ 0 & 1 & 1 \end{bmatrix} & \qquad \text{(b)} \begin{bmatrix} 3 & 0 & -2 & 5 \\ 7 & 1 & 4 & -3 \\ 0 & -2 & 1 & 7 \end{bmatrix} \\
6. \text{ (a)} \begin{bmatrix} 0 & 3 & -1 & -1 & -1 \\ 5 & 2 & 0 & -3 & -6 \end{bmatrix} & \qquad \text{(b)} \begin{bmatrix} 3 & 0 & 1 & -4 & 3 \\ -4 & 0 & 4 & 1 & -3 \\ -1 & 3 & 0 & -2 & -9 \\ 0 & 0 & 0 & -1 & -2 \end{bmatrix}
\end{align*}
