[tex]6cos(x)+3\sqrt{3} =0\\\\6cos(x)= -3\sqrt{3}\\cos(x)= -3\sqrt{3}/6\\cos(x)= -\sqrt{3}/2\\x=(+/-)5\pi /6 +2\pi n\\x_{1} = 5\pi /6 +2\pi n\\ x_{2} =\pi /6 +2\pi n\\[/tex]