Is: $\displaystyle g:[-1,1]=>[0,\pi]$ defined by: $\displaystyle g(x)=arccos(x)$ The value of $\displaystyle g=-\frac{1}{2}$ is:

a) $\displaystyle \frac{2\pi}{3}$

b) $\displaystyle -\frac{2\pi}{3}$

c) $\displaystyle \frac{\pi}{3}$

d) $\displaystyle -\frac{\pi}{3}$

e) $\displaystyle \frac{\pi}{6}$