Answer
$\frac{\pi}{3}$, $\frac{5\pi}{3}$
Work Step by Step
$\sec t=\frac{1}{\cos t}=2$
$\implies \cos t=\frac{1}{2}$
From Figure 22, we find that
$\cos \frac{\pi}{3}=\cos \frac{5\pi}{3}=\frac{1}{2}$
Therefore, the required angles are $ \frac{\pi}{3}$ and $\frac{5\pi}{3}$.
