\begin{exercise}{A2}{Standard matrices}{0010}
\begin{exerciseStatement}
\begin{enumerate}[(a)]
\item Find the standard matrix for the linear transformation \(S:\mathbb{R}^ 4 \to \mathbb{R}^ 2 \) given by \[S\left( \left[\begin{array}{c}
x_{1} \\
x_{2} \\
x_{3} \\
x_{4}
\end{array}\right] \right) = \left[\begin{array}{c}
x_{1} + 2 \, x_{2} - 4 \, x_{3} - x_{4} \\
-2 \, x_{1} - 3 \, x_{2} + 6 \, x_{3}
\end{array}\right] .\]
\item Let \(T:\mathbb{R}^ 4 \to \mathbb{R}^ 1 \) be the linear transformation given by the standard matrix \[ \left[\begin{array}{cccc}
1 & 2 & -3 & -3
\end{array}\right] .\] Compute \(T\left( \left[\begin{array}{c}
-7 \\
-7 \\
-2 \\
2
\end{array}\right] \right)\).
\end{enumerate}
\end{exerciseStatement}
\begin{exerciseAnswer}
\begin{enumerate}[(a)]
\item \[ \left[\begin{array}{cccc}
1 & 2 & -4 & -1 \\
-2 & -3 & 6 & 0
\end{array}\right] \]
\item \[T\left( \left[\begin{array}{c}
-7 \\
-7 \\
-2 \\
2
\end{array}\right] \right)= \left[\begin{array}{c}
-21
\end{array}\right] \]
\end{enumerate}
\end{exerciseAnswer}
\end{exercise}