Consider the following discrete$-$time LTI system

$x[k+1]=Ax[k]$

$y[k]=Cx[k]$

where

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

and

$C=\left[\begin{array}{cc}{c}_1& c_2\end{array}\right]$

Argue that no matter what value you will choose for $c_1$ and $c_2$ the system is always unobservable.