[tex]cos120^{o} = cos(90^{o}+30^{o}) = -sin30^{o} = -\frac{1}{2}\\\\sin150^{o} = sin(90^{o}+60^{o}) = cos60^{o} = \frac{1}{2}\\\\tg120^{o} = tg(90^{o}+30^{o}) = -ctg30^{o} = -\sqrt{3}[/tex]
[tex]\frac{cos120^{o}-sin150^{o}}{tg120^{o}} = \frac{-sin30^{o}-cos60^{o}}{-ctg30^{o}} = \frac{-\frac{1}{2}-\frac{1}{2}}{-\sqrt{3}} = \frac{1}{\sqrt{3}}\cdot\frac{\sqrt{3}}{\sqrt{3}} = \frac{\sqrt{3}}{3}[/tex]
