The solution of $(D^2 + 16)$ $y = cos4x$ is
If \(\omega\) is a complex cube root of unity, then $ \begin{vmatrix} 1 & \omega& \omega^2 \\[0.3em] \omega& \omega^2 & 1 \\[0.3em] \omega^2 & 1& \omega \end{vmatrix}$ is equal to