[tex]\displaystyle \sf 2\cdot cos \ x+\sqrt{3}\leq0 \ \ \ ;\ \ 0\leq x<2\pi \\\\ 2 \cdot cos \ x \leq -\sqrt{3} \\\\ cos \ x\leq \frac{-\sqrt{3}}{2} \\\\\\ cos\ x \leq cos \left(\frac{5\pi}{6} \right) \ \ \ ou \ \ \ cos\ x\leq cos \left(\frac{7\pi}{6} \right) \\\\\\ \underline{{Fazendo \ a \ interse{\c c}{\~a}o\ dos \ intervalos}} \\\\ cos \left(\frac{5\pi}{6} \right) \leq cos \ x \leq cos \left(\frac{7\pi}{6} \right) \\\\\\[/tex]
[tex]\displaystyle \boxed{\sf \left\{ x\in\mathbb{R}\ | \ \frac{5\pi }{6} \leq x \leq \frac{7\pi }{6} \right\}\ } \checkmark[/tex]
letra (a)
