If the matrix A = \(\left[\begin{array}{cc}\cos \theta & \sin \theta \\ -\sin \theta & \cos \theta\end{array}\right]\), then \(A ^2\) is equal to:

1. A \(\left[\begin{array}{cc}\cos 2 \theta & \sin 2 \theta \\ -\sin 2 \theta & \cos 2 \theta\end{array}\right]\)
2. B \(\left[\begin{array}{cc}\cos ^2 \theta & \sin ^2 \theta \\ -\sin ^2 \theta & \cos ^2 \theta\end{array}\right]\)
3. C \(\left[\begin{array}{cc}\cos \theta^2 & \sin \theta^2 \\ -\sin \theta^2 & \cos \theta^2\end{array}\right]\)
4. D \(\left[\begin{array}{ll}\cos \theta+\sin \theta & \cos \theta-\sin \theta \\ \sin \theta-\cos \theta & \cos \theta+\sin \theta\end{array}\right]\)