It is given that \(\lambda\) is an eigenvalue of the matrix \(\mathbf{A}\) with \(\mathbf{e}\) as a corresponding eigenvector, and \(\mu\) is an eigenvalue of the matrix \(\mathbf{B}\) for which \(\mathbf{e}\) is also a corresponding eigenvector.
- Show that \(\lambda + \mu\) is an eigenvalue of the matrix \(\mathbf{A} + \mathbf{B}\) with \(\mathbf{e}\) as a corresponding eigenvector. [2]
The matrix \(\mathbf{A}\), given by
$$\mathbf{A} = \begin{pmatrix} 2 & 0 & 1 \\ -1 & 2 & 3 \\ 1 & 0 & 2 \end{pmatrix}$$
has \(\begin{pmatrix} 1 \\ 2 \\ 1 \end{pmatrix}\), \(\begin{pmatrix} 1 \\ 4 \\ -1 \end{pmatrix}\) and \(\begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix}\) as eigenvectors.
- Find the corresponding eigenvalues. [3]
The matrix \(\mathbf{B}\) has eigenvalues \(4\), \(5\) and \(1\) with corresponding eigenvectors \(\begin{pmatrix} 1 \\ 2 \\ 1 \end{pmatrix}\), \(\begin{pmatrix} 1 \\ 4 \\ -1 \end{pmatrix}\) and \(\begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix}\) respectively.
- Find a matrix \(\mathbf{P}\) and a diagonal matrix \(\mathbf{D}\) such that \((\mathbf{A} + \mathbf{B})^3 = \mathbf{P}\mathbf{D}\mathbf{P}^{-1}\). [3]