Explain how to find a basis for the eigenspace associated to the eigenvalue \( -1 \) in the matrix
\[ \left[\begin{array}{cccc} -2 & -1 & 0 & 1 \\ -2 & -4 & 4 & 6 \\ -2 & -2 & 0 & 3 \\ -1 & -2 & 3 & 3 \end{array}\right] \]
Answer:
\[\operatorname{RREF} \left[\begin{array}{cccc} -1 & -1 & 0 & 1 \\ -2 & -3 & 4 & 6 \\ -2 & -2 & 1 & 3 \\ -1 & -2 & 3 & 4 \end{array}\right] = \left[\begin{array}{cccc} 1 & 0 & 0 & -1 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 1 \\ 0 & 0 & 0 & 0 \end{array}\right] \]
A basis of the eigenspace is \( \left\{ \left[\begin{array}{c} 1 \\ 0 \\ -1 \\ 1 \end{array}\right] \right\} \).