Answer
$s=\dfrac{11\pi}{6}$
Work Step by Step
Use the inverse cosine function of a calculator in radian mode to obtain:
$s =\cos^{-1}{(\frac{\sqrt3}{2})}=\frac{\pi}{6}$
The angle must be within the interval $[\frac{3\pi}{2}, 2\pi]$
Note $\cos{(\frac{\pi}{6})}=\cos{(-\frac{\pi}{6})}$.
Since $\cos{\theta} = \cos{(\theta+2\pi)}$, then
$\cos{(-\frac{\pi}{6})}=\cos{(-\frac{\pi}{6}+2\pi)}=\cos{(\frac{11\pi}{6})}$
Thus,
$s=\dfrac{11\pi}{6}$
