# How do you evaluate cos((-4pi)/3)?

$- \frac{1}{2}$
$\cos \left(\frac{- 4 \pi}{3}\right) = \cos \left(\frac{4 \pi}{3}\right) = \cos \left(\frac{\pi}{3} + \pi\right) = - \cos \left(\frac{\pi}{3}\right) = - \frac{1}{2}$