I would like to show you a proof for the integral,
∫01xb−1(1−x)c−b−1ln(x)dx
It is for the proving of my previous discussion,"On the Summation of Hypergeometric series".
Observe,
dbd(B(b,c−b))=∫01xb−1(1−x)c−b−1(ln(x)−ln(1−x))dx
Then by splitting the integral we get,
dbd(B(b,c−b))=∫01xb−1(1−x)c−b−1ln(x)dx−∫01xb−1(1−x)c−b−1ln(1−x)dx
We have our integral but with an additional integral,for that lets use this integral.Since,
B(b,c−b)=∫01xb−1(1−x)c−b−1dx
Then taking d.w.r.c,we get,
dcd(B(b,c−b))=∫01xb−1(1−x)c−b−1ln(1−x)dx
And hey! That's our required equation.So,
dbd(B(b,c−b))+dcd(B(b,c−b))=∫01xb−1(1−x)c−b−1ln(x)dx
So the only thing left is to find the value of the derivative,which is quite easy once you have the knowledge of beta function and the diagamma function,
dbd(B(b,c−b))=B(b,c−b)(ψ(b)−ψ(c−b)),dcd(B(b,c−b))=B(b,c−b)(ψ(c−b)−ψ(c))
Then adding both derivative we have,
∫01xb−1(1−x)c−b−1ln(x)dx=B(b,c−b)(ψ(b)−ψ(c))
And as our corollary ,(I love corollary),
∫01xb−1(1−x)−bln(x)dx=sin(πb)π(ψ(b)+γ)
Where γ is Euler constant about 0.577.
#Calculus
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