Let A be a square matrix defined by \( A = \begin{pmatrix}-2&-1&-5\\ 2&2&3\\ 4&2&2\end{pmatrix} \)
(a) Find the characteristic polynomial of A.
(b) Find the eigenvalues and eigenspaces of A.
(c) Show that A is not diagonalizable, but it is triangularizable, then triangularize A.
(d) Find the three real sequences \( (a)_n, (b)_n ,(c)_n \) satisfying.
\( \begin{cases}
a_{n+1}=-2a_n-b_n-5c_n \hspace{2mm},a_0=1 & \quad \\
b_{n+1}=2a_n+2b_n+3c_n \hspace{2mm}, b_0=0 & \quad \\
c_{n+1}=4a_n+2b_n+6c_n \hspace{2mm},c_0=1 & \quad
\end{cases} \)