Answer
$\ln 3$
Work Step by Step
Substitute into the relevant formula:
$\displaystyle \cosh^{-1}(\frac{5}{3})=\ln(\frac{5}{3}+\sqrt{\frac{25}{9}-1})$
$=\displaystyle \ln(\frac{5}{3}+\sqrt{\frac{16}{9}})$
$=\displaystyle \ln(\frac{5}{3}+\frac{4}{3})$
= $\ln 3$
