Question
Integrate the following functions w.r.t. x:

$\frac{1}{x \cdot \log x \cdot \log (\log x)}$

Answer

Let $I=\int \frac{1}{x \cdot \log x \cdot \log (\log x)} d x$

$=\int \frac{1}{\log (\log x)} \cdot \frac{1}{x \cdot \log x} d x$

Put $\log (\log x)=t \quad \therefore \frac{1}{\log x} \cdot \frac{1}{x} d x=d t$

$\therefore \frac{1}{x \cdot \log x} d x=d t$

$\begin{aligned} \therefore I & =\int \frac{1}{t} d t=\log |t|+c \\ & =\log |\log (\log x)|+c .\end{aligned}$

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