[tex]z=cos\dfrac{\pi}{6}-isin\dfrac{\pi}{6}=cos(\dfrac{-\pi}{6})+isin(\dfrac{-\pi}{6})=[/tex]
[tex]=cos(2\pi-\dfrac{\pi}{6})+isin(2\pi-\dfrac{\pi}{6})=cos(\dfrac{11\pi}{6})+isin(\dfrac{11\pi}{6})[/tex]
Deci: [tex]arg \ z=\dfrac{11\pi}{6}\in[0;2\pi);\ Arg z=\{2k\pi+\dfrac{11\pi}{6}|\ k\in Z\}[/tex]