Calculus: Early Transcendentals 8th Edition

$x = \frac{\pi}{3}~~$ or $~~x = \frac{5\pi}{3}$
We can find the values of $x$: $2~cos~x - 1 = 0$ $2~cos~x = 1$ $cos~x = \frac{1}{2}$ $x = \frac{\pi}{3}~~$ or $~~x = \frac{5\pi}{3}$