Mathematics

Problem

Find the principal solutions of

\cos x = \dfrac12

in the interval

[0,2\pi)

. a)

x = \dfrac{\pi}{6},\ \dfrac{11\pi}{6}

x = \dfrac{2\pi}{3},\ \dfrac{4\pi}{3}

x = \dfrac{\pi}{3},\ \dfrac{5\pi}{3}

x = \dfrac{\pi}{3},\ \dfrac{4\pi}{3}