Answer
$\dfrac{\pi}{3}, \dfrac{5\pi}{3}$
Work Step by Step
Since $\cos{\theta}$= x-coordinate
From figure 22, angles $\dfrac{\pi}{3}$ and $\dfrac{5\pi}{3}$ have a x-coordinate of $\dfrac{1}{2}$ on the unit circle
$\theta= \dfrac{\pi}{3}, \dfrac{5\pi}{3}$
