\Leftrightarrow 1+ \sin 2x - \cos x = \cos x + 2\sin x\Leftrightarrow 1- \sin x + (\sin2x - \sinx) - ( \cos2x + \cosx)= 0
\Leftrightarrow (\sin\frac{x}{2} - \cos\frac{x}{2})( \sin \frac{x}{2} - \cos \frac{x}{2} + 2\cos \frac{3x}{2}) = 0
khuc nay` thi ai cung biet