Friday, November 4, 2016

calculus - Old & cool integral intpi0sinb1(x)sin(ax)dx=fracpisin(api/2)2b1bBleft(fracb+a+12,fracba+12right)

Here is an integral that appears in the table of integrals by Gradshtein and Ryzhik, it was also studied by Ramanujan (not sure his original solution was found - it seems it doesn't appear in
any of the notebooks).


π0sinb1(x)sin(ax) dx=πsin(aπ/2)2b1bB(b+a+12,ba+12)


Now, by complex analysis, one can brifely finish it, I'm not interested in such a solution. But thinking of Ramanujan I'm sure he had a solution using methods of real analysis (and to avoid
possible misunderstandings, I mean not even a touch on complex numbers - to be clear).


Do you know such a solution? Post it only if you want to, I'm only curious if such solutions are known, maybe some simple such solutions?


Application of the integral above (supplementary question)


Prove that


π/20log(sin(x))+xcsc2(x)xcot(x)x2+log2(sin(x))dx=Si(π2),


http://mathworld.wolfram.com/SineIntegral.html



or simply show that


π/20xcot(x)log(sin(x))x2+log2(sin(x))dx=π2.

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