Answer
$s = \displaystyle \frac{11\pi}{6}$
Work Step by Step
For any real number $s$ represented by a directed arc on the unit circle,
$\sin s=y\quad \cos s=x \quad \displaystyle \tan s=\frac{y}{x} (x\neq 0)$
Use Figure 13 on page 111.
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In the interval $[\displaystyle \frac{3\pi}{2},2\pi]$, (quadrant IV), we search for
a point (x,y) on the unit circle, such that $x=\displaystyle \frac{\sqrt{3}}{2}$
$(\cos s=x)$
We find the point$:$
$(\displaystyle \frac{\sqrt{3}}{2},-\frac{1}{2}) \quad $assigned to $330^{o}$, or $\displaystyle \frac{11\pi}{6}$ rad.
$\displaystyle \cos\frac{11\pi}{6}=x=\frac{\sqrt{3}}{2}$
$s = \displaystyle \frac{11\pi}{6}$
