d. \( (8 \mathrm{pts}) \) Verify that \( X=\left[\begin{array}{cccc}1 & -1 & -7 & 0 \\ 0 & 1 & 2 & -1 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & -2\end{array}\right] \) is the matrix of eigenvectors and determine which eigenvalue corresponds to each column vector from \( X \). (Hint: use \( A \mathbf{x}_{i}=\lambda_{i} \mathbf{x}_{i}, i=1,2,3 \) and 4 such that the eigenvalues match the answers from (b))
e. ( 6 pts ) Determine whether \( X \) is singular or invertible. If invertible, find \( X^{-1} \) using either Gauss-Jordan elimination or the matrix of cofactors.
f. (1 pts) Based on your results of part (d) and without calculation write the product of \( X^{-1} A X \).