Is it possible the cos^-1 and the cos cancel leaving the answer as $\displaystyle 4PI/3$?
You know that $\displaystyle \frac{4 \pi}{3}$ does not lie in the range of $\displaystyle \cos^{-1}$, so it cannot be the correct answer. (However, whoever wrote the question might not realise this .....)
You know that $\displaystyle \frac{4 \pi}{3}$ does not lie in the range of $\displaystyle \cos^{-1}$, so it cannot be the correct answer. (However, whoever wrote the question might not realise this .....)
That is true, still hoping I overlooked something simple. The author of the question may not be aware of this?