# Math Help - question about inverse trig

1. ## question about inverse trig

Find the exact value of arccos(cos4Pi3)
There is meant to be an arrow above the three..

What would the arrow above the three represent? and how would i solve that question

2. An arrow over a number makes no sense! Normally, an arrow over a letter indicates a vector but then it cannot be a number. I rather suspect that it is actually a "/" indicating ordinary division: $cos^{-1}(cos(4\pi/3))$. $4\pi/3$ is outside the natural range of arccosine, which is 0 to $\pi$ so $cos^{-1}(cos(4\pi/3))= 2\pi- 4\pi/3= 2\pi/3$.