Hi all, i wonder if anyone can help me with this question, tried and failed&im wasting too much time on this one!

Determine the arc lenth of:

$\displaystyle

\begin{gathered}

y = \ln \cos ecx \hfill \\

x = \frac{\pi }

{4} \hfill \\

x = \frac{\pi }

{3} \hfill \\

\end{gathered}

$

between those limits