Ans: (C)
If \(Q(\theta)=\left[\begin{array}{c}\cos \theta-\sin \theta \\ \sin \theta \\ \cos \theta\end{array}\right], Q^{3}(\theta)=Q(3 \theta), Q^{3}(\pi / 4)=\left[\begin{array}{cc}\cos 3 \pi / 4 & -\sin 3 \pi / 4 \\ \sin 3 \pi / 4 & \cos 3 \pi / 4\end{array}\right]=\left[\begin{array}{cc}-1 / \sqrt{2} & -11 / \sqrt{2} \\ 1 / \sqrt{2} & -1 / \sqrt{2}\end{array}\right], Q^{3}(\pi / 4) x=\left(\begin{array}{l}-1 \\ 0\end{array}\right)\)