Exercise 2.3.6

Example: $\left[\begin{array}{ccc}2\hfill & 3\hfill & 7\hfill \\ 2\hfill & 3\hfill & 7\hfill \\ 2\hfill & 3\hfill & 7\hfill \end{array}\right]\left[\begin{array}{c}\hfill 1\\ \hfill 3\\ \hfill -1\end{array}\right]=\left[\begin{array}{c}4\hfill \\ 4\hfill \\ 4\hfill \end{array}\right]$. If all columns are multiples of column 1, there is no second pivot.