0002.ptx

<exercise checkit-seed="0002" checkit-slug="M3" checkit-title="Invertible matrices">
  <statement>
    <p>Explain why the matrix <m>N= \left[\begin{array}{cccc}
1 &amp; -2 &amp; 8 &amp; 7 \\
0 &amp; 1 &amp; -2 &amp; -1 \\
1 &amp; -1 &amp; 6 &amp; 7 \\
1 &amp; 0 &amp; 4 &amp; 5
\end{array}\right] </m> is or is not invertible.</p>
  </statement>
  <answer><p><me>\operatorname{RREF} \left[\begin{array}{cccc}
1 &amp; -2 &amp; 8 &amp; 7 \\
0 &amp; 1 &amp; -2 &amp; -1 \\
1 &amp; -1 &amp; 6 &amp; 7 \\
1 &amp; 0 &amp; 4 &amp; 5
\end{array}\right] = \left[\begin{array}{cccc}
1 &amp; 0 &amp; 4 &amp; 0 \\
0 &amp; 1 &amp; -2 &amp; 0 \\
0 &amp; 0 &amp; 0 &amp; 1 \\
0 &amp; 0 &amp; 0 &amp; 0
\end{array}\right] </me></p><m>N</m> is not invertible.</answer>
</exercise>