Find the cigenvalues of the matrices in Exercises $17$ and is:

$17.\left[\begin{array}{ccc}0& 0& 0\\ 0& 2& 5\\ 0& 0& -1\end{array}\right]$

$18.\left[\begin{array}{ccc}8& 0& 0\\ -7& 0& 0\\ 6& -5& -4\end{array}\right]$

$19.$ For $A=\left[\begin{array}{ccc}1& 2& 3\\ 1& 2& 3\\ 1& 2& 3\end{array}\right],$ fin culation. Justify your answer.

$20.$ Without calculation, find one eigenvalue and two linedit independent eigenvectors of $A=\left[\begin{array}{ccc}4& 4& -4\\ 4& 4& -4\\ 4& 4& -4\end{array}\right].$ Jasith your answer.