CP$6\mathrm{.}9$ Consider a system represented in state variable form

where

$x^{}=Ax+Bu$

$y=Cx+Du$

$A=\left[\begin{array}{ccccccc}0& 1& 0& 0& 1& -3& -2\end{array}\right]$

$-k$

$-k$

$2,B=\left[\begin{array}{c}-1\end{array}\right]$

$0$

$1$

$C=\left[\begin{array}{ccc}1& 2& 0\end{array}\right],D=[0]$

$($a$)$ For what values of $k$ is the system stable?