<s>[INST] Prove that : $\int_0^{1}\frac{1-\sqrt{1-x^{4}}}{x^{2}\sqrt{1-x^4}}dx=1-\frac{\sqrt{2}\pi^{\frac{3}{2}}}{\Gamma(\frac{1}{4})^2}$ Prove that :
$$\int_0^{1}\frac{1-\sqrt{1-x^{4}}}{x^{2}\sqrt{1-x^4}}dx=1-\frac{\sqrt{2}\pi^{\frac{3}{2}}}{\Gamma(\frac{1}{4})^2}.$$
I know how to use the definition of the Beta and Gamma functions so my problem here is when I divide the integral I find:
$$\int_0^{1}\frac{1}{x^2}dx=\infty!!$$ 
(divergent)
I tried using $y=\frac{1}{x}$ but didn't get the answer.
I also tried $y=x^{4}$ and got the same problem (a divergent integral).
 [/INST] Substitute $u = x^4$ to get
$$ \int_{0}^{1} \frac{1-\sqrt{1-x^4}}{x^2\sqrt{1-x^4}} \, \mathrm{d}x
= \frac{1}{4} \int_{0}^{1} \frac{1-(1-u)^{1/2}}{u^{5/4}(1-u)^{1/2}} \, \mathrm{d}u. $$
Now we regularize the integral by replacing $u^{5/4}$ by $u^s$ for $s < 1$. Then
\begin{align*}
\frac{1}{4} \int_{0}^{1} \frac{1-(1-u)^{1/2}}{u^{s}(1-u)^{1/2}} \, \mathrm{d}u
&= \frac{1}{4}\left(B\left(1-s,\tfrac{1}{2}\right)-\frac{1}{1-s}\right) \\
&= \frac{1}{4}\left(\frac{\Gamma(1-s)\Gamma\left(\frac{1}{2}\right)}{\Gamma\left(\frac{3}{2}-s\right)}-\frac{1}{1-s}\right).
\end{align*}
Note that the left-hand side defines an analytic function for $\operatorname{Re}(s) < 2$, while the right-hand side is a meromorphic function on all of $\mathbb{C}$ with the removable singularity at $s = 1$. So both sides give rise to analytic functions on $\operatorname{Re}(s) < 2$, and so, they are equal on this region by the principle of analytic continuation. Therefore we can simply plug $s = 5/4$ to get
\begin{align*}
\frac{1}{4} \int_{0}^{1} \frac{1-(1-u)^{1/2}}{u^{5/4}(1-u)^{1/2}} \, \mathrm{d}u
&= 1 + \frac{\Gamma\left(-\frac{1}{4}\right)\Gamma\left(\frac{1}{2}\right)}{4\Gamma\left(\frac{1}{4}\right)} \\
&= 1 - \frac{\Gamma\left(\frac{3}{4}\right)\Gamma\left(\frac{1}{2}\right)}{\Gamma\left(\frac{1}{4}\right)},
\end{align*}
which simplifies to the desired expression by Euler's reflection formula $\Gamma(z)\Gamma(1-z) = \pi\csc(\pi z)$.
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