$.8$ points$)$ Verify by direct computation that the vector function

is a solution to the DE

$Y(t)=\left[\begin{array}{c}-2cos(3t)\end{array}\right]$

$3cos(3t)-3sin(3t)$

$Y^{\text{'}}(t)=\left[\begin{array}{ccc}-3& -2& 3\end{array}\right]$

$9Y(t)$

$($Plug the given $Y$ in to each side separately; Do not solve the DE in general.$)$