Giải phương trình \(1 + \sin x + \cos 3x = \cos x + \sin 2x + \cos 2x.\)
A.\(S = \left\{ {k2\pi ,\,\,\frac{{2\pi }}{3} + \frac{{k2\pi }}{3},\,\,\frac{{ - \pi }}{6} + k2\pi ,\,\,\frac{{7\pi }}{6} + k2\pi ,\,\,k \in \mathbb{Z}} \right\}\)
B.\(S = \left\{ {k2\pi ,\,\,\frac{\pi }{3} + \frac{{k2\pi }}{3},\,\,\frac{{ - \pi }}{6} + k2\pi ,\,\,\frac{{7\pi }}{6} + k2\pi ,\,\,k \in \mathbb{Z}} \right\}\)
C.\(S = \left\{ {k2\pi ,\,\,\frac{{2\pi }}{3} + \frac{{k2\pi }}{3},\,\,\frac{\pi }{6} + k2\pi ,\,\,\frac{{7\pi }}{6} + k2\pi ,\,\,k \in \mathbb{Z}} \right\}\)
D.\(S = \left\{ {k2\pi ,\,\,\frac{\pi }{3} + \frac{{k2\pi }}{3},\,\,\frac{\pi }{6} + k2\pi ,\,\,\frac{{7\pi }}{6} + k2\pi ,\,\,k \in \mathbb{Z}} \right\}\)