$\begin{array}{l} 4\sin^23x + 2(\sqrt3 + 1)\cos3x - \sqrt3 = 0\\ \Leftrightarrow 4(1 - \cos^23x)+ 2(\sqrt3 + 1)\cos3x - \sqrt3 = 0\\ \Leftrightarrow -4\cos^23x + 2(\sqrt3 + 1)\cos3x + 4 -\sqrt3 = 0\\ \Leftrightarrow \left[\begin{array}{l}\cos3x \approx -0,3336\\\cos3x \approx 1,6996\,\,\,(loại)\end{array}\right.\\ \Leftrightarrow x = \pm \dfrac{\arccos(-0,3336)}{3} + k\dfrac{2\pi}{3}\,\,\,\,\,(k \in \Bbb Z)\end{array}$
