TITLE: Compute the following integral: $I = \int_1^\infty \log^2 \left(1-\frac 1 x\right) \, dx$
QUESTION [9 upvotes]: Compute $$I = \int_1^\infty \log^2 \left(1-\frac 1 x\right) \, dx$$
I made the substitution: $$t=\frac 1 x$$ It follows:
$$I=\int_0^1 \frac{\log^2(1-t)}{t^2} \, dt$$
My next step would be to compute the derivative of the following integral with parameter $y$, w.r.t to $y$:
$$F(y)=\int_0^1 \frac{\log^2(y-t)}{t^2} \, dt$$
Or something like this. I think would be a nice solution to use this kind of approach. But I am getting stuck after computing the derivative.

REPLY [10 votes]: I thought it might be instructive to present an approach that relies on integration by parts and recognition of the value of the integral, $\int_0^1 \frac{\log(1-x)}{x}\,dx=\text{Li}_2(1)=\frac{\pi^2}{6}$.  To that end, we proceed.


Let $I$ be given by 
$$I=\int_1^\infty \log^2\left(1-\frac1x\right)\,dx=\int_0^1\frac{\log^2(1-x)}{x^2}\,dx$$
Integrating by parts with $u=\log^2(1-x)$ and $v=-1/x$ reveals
$$\begin{align}
I&=\lim_{\epsilon\to 0}\left(\left.\left(-\frac{\log^2(1-x)}{x}\right)\right|_{0}^{1-\epsilon}-2\int_0^{1-\epsilon}\frac{\log(1-x)}{x(1-x)}\,dx\right)\\\\
&=\lim_{\epsilon\to 0}\left(\frac{-\log^2(\epsilon)}{1-\epsilon}-2\int_0^{1-\epsilon}\frac{\log(1-x)}{1-x} -2\int_0^1\frac{\log(1-x)}{x}\,dx\right)\\\\
&=\lim_{\epsilon\to 0}\left(-\frac{\log^2(\epsilon)}{1-\epsilon}+2\int_0^{1-\epsilon}\frac12\frac{d\log^2(1-x)}{dx}\,dx -2\int_0^1\frac{\log(1-x)}{x}\,dx\right)\\\\
&=-2\int_0^1\frac{\log(1-x)}{x}\,dx\\\\
&=\frac{\pi^2}{3}
\end{align}$$
as was to be shown!