How do you find cos x= -1/2?

Aug 14, 2015

cos x = - 1/2 = cos 2$\pi$ /3 $\implies$ x = 2$\pi$ /3

Explanation:

Cosine negative in the second quadrant. cos $\pi$/3 = 1/2.
cos ($\pi$ - $\theta$ )= - cos$\theta$