How do you find the exact value of cos^-1(cos((5pi)/3))?

${300}^{o}$
${\cos}^{- 1} \cos x$ equals x, hence the given expression equals $\frac{5 \pi}{3} = 5 \left(\frac{180}{3} \mathrm{de} g r e e s\right) = {300}^{o}$
($\pi$ radians equal ${180}^{o}$)