# Closed form 0f $I=\int _{ 0 }^{ 1 }{ \frac { \ln { x } { \left( \ln { \left( 1-{ x }^{ 2 } \right) } \right) }^{ 3 } }{ 1-x } dx }$

While solving a problem, I got stuck at an integral. The integral is as follows:

Find the closed form of: $$I=\int _{ 0 }^{ 1 }{ \frac { \ln { x } { \left( \ln { \left( 1-{ x }^{ 2 } \right) } \right) }^{ 3 } }{ 1-x } dx }$$

I tried using power series but it failed. I tried various subtitutions which came to be of no use. Please help.

• Why do you believe that this has a closed form solution? – Mark Viola Feb 26 '16 at 5:16
• @Dr.MV I believe so because the question which I was solving had a good closed form. – Aditya Kumar Feb 26 '16 at 5:21
• And how does that "question I was solving" relate to this integral? Just FYI ... one does not solve a question; one answers a question. ;-)) – Mark Viola Feb 26 '16 at 5:26
• Thanks for correcting me @Dr.MV – Aditya Kumar Feb 26 '16 at 6:08
• @MhenniBenghorbal I tried to use the power series of ln(1-x) and of 1/(1-x). It tried to get it to a form of harmonic numbers but I failed – Aditya Kumar Feb 26 '16 at 6:13

We have $$I=\int_{0}^{1}\frac{\log\left(x\right)\log^{3}\left(1-x^{2}\right)}{1-x}dx=\int_{0}^{1}\frac{\log\left(x\right)\log^{3}\left(1-x^{2}\right)}{1-x^{2}}dx+\int_{0}^{1}\frac{x\log\left(x\right)\log^{3}\left(1-x^{2}\right)}{1-x^{2}}dx$$ and so if we put $x=\sqrt{y}$ we get $$I=\frac{1}{4}\int_{0}^{1}\frac{y^{-1/2}\log\left(y\right)\log^{3}\left(1-y\right)}{1-y}dy+\frac{1}{4}\int_{0}^{1}\frac{\log\left(y\right)\log^{3}\left(1-y\right)}{1-y}dy$$ and recalling the definition of beta function $$B\left(a,b\right)=\int_{0}^{1}x^{a-1}\left(1-x\right)^{b-1}dx$$ we have $$\frac{\partial^{h+k}B}{\partial a^{h}\partial b^{k}}\left(a,b\right)=\int_{0}^{1}x^{a-1}\log^{h}\left(x\right)\left(1-x\right)^{b-1}\log^{k}\left(1-x\right)dx$$ hence $$I=\frac{1}{4}\frac{\partial^{4}B}{\partial a\partial b^{3}}\left(\frac{1}{2},0^{+}\right)+\frac{1}{4}\frac{\partial^{4}B}{\partial a\partial b^{3}}\left(1,0^{+}\right).$$ For the computation of the limit, we can use the asymptotic $\Gamma(x)=\frac{1}{x}+O(1)$ when $x\rightarrow 0$ and the relations between the polygamma terms and zeta.
• Brilliant, since it can easily be generalized ! :-$)$ – Lucian Mar 1 '16 at 8:43
The closed form is $$I=21\zeta({3})\log^22-\pi^2\log^32-\frac{13}{4}\pi^2\zeta({3})+48\zeta({5})-\frac{1}{4}\pi^4\log2$$
• I based on my study of the integrals of the form $$\int_0^1\frac{\log{x}^p\log({1-x})^q\log{1+x})^r}{1±x}dx\ with\ p+q+r=4$$ Also $$\int _{ 0 }^{ 1 }{ \frac { \ln { x } { \left( \ln { \left( 1-{ x }^{ 2 } \right) } \right) }^{ 3 } }{ 1-x } dx }- \int _{ 0 }^{ 1 }{ \frac { \ln { x } { \left( \ln { \left( 1-{ x }^{ 2 } \right) } \right) }^{ 3 } }{ 1+x } dx } =3\zeta({5})$$ – user178256 Feb 26 '16 at 23:07
• The two values coincide for the first $100$ decimals, which, given the reduced complexity of the expression, removes all reasonable doubt as to its veracity. – Lucian Feb 27 '16 at 0:55