The given function is:
[tex]y=\ln (\sinh 9z)[/tex]Differentiate w. r. t. z to get:
[tex]\begin{gathered} \frac{dy}{dz}=\frac{d}{dz}(\ln \sinh 9z) \\ =\frac{1}{\sinh9z}\frac{d}{dz}(\sinh 9z) \\ =\frac{1}{\sinh9z}\cosh 9z(\frac{d}{dz}9z) \\ =\frac{9\cosh 9z}{\sinh 9z} \\ =9\cot h9z \end{gathered}[/tex]Hence the derivative is 9cot9z.
