[latex]2cosx+ sqrt{3}=0 \ 2cosx=- sqrt{3} \ cosx= -frac{ sqrt{3} }{2} \ x=pm arccos(-frac{ sqrt{3} }{2} )+2pi n \ x=pm(pi -arccos frac{ sqrt{3} }{2})+2pi n \ x=pm(pi- frac{pi}{4} )+2pi n \ x=pm frac{3pi}{4} +2pi n, nin Z[/latex]