# How to calculate one integral in terms of another given one?

by infinite-blank-   Last Updated July 12, 2019 09:20 AM - source

We are given that $$\int_{0}^\infty e^{-x^2}\,dx=\alpha$$ then we need to find the value of $$\int_{0}^{1}\sqrt{|\ln x|}\,dx$$ in terms of $$\alpha$$.

What I did was to integrate the second integral by parts taking $$1$$ as the first function and $$\sqrt{|\ln x|}$$ as the second.

This gave me $$\big[\sqrt{\ln x}+x\big]_{0}^{1}-\frac12\int\frac{1}{\sqrt{\ln x}}\,dx$$

But I'm stuck after this. I can't see what I should do to bring the above integral into play. Can someone suggest something to move ahead or maybe some other method?

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Let $$t=\sqrt{|\ln x|}$$ for $$0, then $$x=e^{-t^2}$$ and thus $$\int_0^1 \sqrt{|\ln x|}\,dx=-\int_0^\infty t\,d(e^{-t^2})=-te^{-t^2}\mid_0^\infty+\int_0^\infty e^{-t^2}\,dt=\alpha.$$