Question

Find the value of $\theta ,0\le \theta \le 2\pi$ for which $\cos \theta =-1/2$

Answer 1

$cos\theta =\frac{-1}{2}$

=> $cos\theta =cosx$

=> $\theta =2n{\pi }_{-}^{+}x$

=> $\theta =2n{\pi }_{-}^{+}\frac{2\pi }{3}$

For, given condition

Put values of $n$,

We get,

$\theta =\frac{2\pi }{3},\frac{4\pi }{3}$