5.
$$\mathbf { M } = \left( \begin{array} { r r r }
1 & 2 & k
- 1 & - 3 & 4
2 & 6 & - 8
\end{array} \right) \quad \text { where } k \text { is a constant }$$
Given that \(\mathbf { M }\) has a repeated eigenvalue, determine
- the possible values of \(k\),
- all corresponding eigenvalues of \(\mathbf { M }\) for each value of \(k\).