# What is the value of cos sign if the reference angle is 13 pi/3?

$\frac{1}{2}$
$\frac{13 \pi}{3} = \frac{\pi}{3} + 4 \pi$
$\cos \left(\frac{13 \pi}{3}\right) = \cos \left(\frac{\pi}{3} + 4 \pi\right) = \cos \left(\frac{\pi}{3}\right)$
$\cos \left(\frac{\pi}{3}\right)$ is positive and equals to --> $\cos \left(\frac{\pi}{3}\right) = \frac{1}{2}$.