0006.ptx

<exercise checkit-seed="0006" checkit-slug="M3" checkit-title="Invertible matrices">
  <statement>
    <p>Explain why the matrix <m>A= \left[\begin{array}{cccc}
-1 &amp; -1 &amp; 7 &amp; 1 \\
1 &amp; 0 &amp; -2 &amp; 3 \\
-1 &amp; 0 &amp; 3 &amp; -2 \\
-1 &amp; 1 &amp; -4 &amp; -7
\end{array}\right] </m> is or is not invertible.</p>
  </statement>
  <answer><p><me>\operatorname{RREF} \left[\begin{array}{cccc}
-1 &amp; -1 &amp; 7 &amp; 1 \\
1 &amp; 0 &amp; -2 &amp; 3 \\
-1 &amp; 0 &amp; 3 &amp; -2 \\
-1 &amp; 1 &amp; -4 &amp; -7
\end{array}\right] = \left[\begin{array}{cccc}
1 &amp; 0 &amp; 0 &amp; 0 \\
0 &amp; 1 &amp; 0 &amp; 0 \\
0 &amp; 0 &amp; 1 &amp; 0 \\
0 &amp; 0 &amp; 0 &amp; 1
\end{array}\right] </me></p><m>A</m> is invertible.</answer>
</exercise>