\ker \left( {A - I} \right) = \left\{ {\left[ {\begin{array}{*{20}c}
{x_1 } \\
{x_2 } \\
{x_3 } \\
\end{array} } \right]:\left[ {\begin{array}{*{20}c}
0 & 2 & 3 \\
0 & 0 & 2 \\
0 & 0 & 1 \\
\end{array} } \right]\left[ {\begin{array}{*{20}c}
{x_1 } \\
{x_2 } \\
{x_3 } \\
\end{array} } \right] = \left[ {\begin{array}{*{20}c}
0 \\
0 \\
0 \\
\end{array} } \right]} \right\} = |