complex numbers

First of all if the principal argument of a complex number is \theta then -\pi < \theta \leq \pi.

Over here after rationalisation we get,

z=\frac{-1}{2}-\frac{\sqrt{3}}{2}i

\theta =\tan^{-1}\left( \frac{Im(z)}{Re(z)}\right) = \tan^{-1}\sqrt{3}=\frac{\pi }{3}

Now, since both Re(z)<0 and Im(z)<0, the complex number must lie in the third quadrant of the argand plane.

Therefore, Arg(z)= \theta -\pi =-\frac{2\pi }{3}

-2pi/3 = - 120° not 240°

120

so.. what is the correct ans????? 120°???

-120 is the right answer