A) \[\frac{9\pi }{3}\]
B) \[\frac{8\pi }{3}\]
C) \[\frac{5\pi }{3}\]
D) \[\frac{11\pi }{3}\]
Correct Answer: B
Solution :
Let \[\theta ={{\cos }^{-1}}\left( \frac{-1}{2} \right)\] \[\Rightarrow \] \[\cos \,\theta =-\frac{1}{2}=-\cos \,\left( \frac{\pi }{3} \right)\] \[=\cos \left( \pi -\frac{\pi }{3} \right)=\cos \,\left( \frac{2\pi }{3} \right)\] \[\Rightarrow \] \[\theta =2n\pi \pm \frac{2\pi }{3}\] \[\Rightarrow \] \[\theta =\frac{4\pi }{3},\frac{8\pi }{3},\frac{10\pi }{3},\frac{14\pi }{3},...............\]
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