For $4\times 5$ matrix which is, $$ \begin{bmatrix} 2 &-3 &4 &1 &0\\ 0 & 6& 6 &1 &3\\ 0 & 0& 0 &1 &9\\ 0 & 0& 0& 0& 0 \end{bmatrix} $$ I made it as RREF that is,
$$\begin{bmatrix} 1& 3/2 &5 &1 &0\\ 0 &1& 1& 1/6& 1/2\\ 0 &0& 0& 1& 9\\ 0& 0& 0& 0& 0\\ \end{bmatrix}$$ I know the first column is the basis for the column space, but I do not understand why the second and fourth columns are also basis for the column space... isn`t leading 1 representing a column that has only one value that is 1? Please help...