sin x + cos(2x + pi/3) = 0 giúp mình với ạ

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sin x + cos (2x + $\frac{\pi}{3}$) = 0 $\\$ <=> cos (2x + $\frac{\pi}{3}$) = -sin x $\\$ <=> cos (x + $\frac{\pi}{3}$) = cos ($\frac{\pi}{2}$ + x) $\\$ <=> $\left[\begin{matrix} 2x + \frac{\pi}{3} = \frac{\pi}{2} + x + k.2\pi\\ 2x + \frac{\pi}{3} = -\frac{\pi}{2} - x + k.2\pi\end{matrix}\right.$ (K $\in$ $\mathbb{Z}$) $\\$ <=> $\left[\begin{matrix} x = \frac{\pi}{6} + k.2\pi\\ 3x = -\frac{5\pi}{6} + k.2\pi\end{matrix}\right.$ (K $\in$ $\mathbb{Z}$) $\\$ <=> $\left[\begin{matrix} x = \frac{\pi}{6} + k.2\pi\\ x = -\frac{5\pi}{18} + \frac{k.2\pi}{3}\end{matrix}\right.$ (K $\in$ $\mathbb{Z}$)

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