## Calculus (3rd Edition)

$$y'= \frac{3}{x\ln x}.$$
Recall that $(\ln x)'=\dfrac{1}{x}$ Since $y=\ln (\ln x)^3$, first we simplify $y$ as follows $$y=3\ln (\ln x)$$ then by the chain rule, we have $$y'=3\frac{1/x}{\ln x}=\frac{3}{x\ln x}.$$