Is there any simple way to get this integral? I'm also using Wolfram Alpha, but I get the solution below. I need specific answer not function that depends on a summation like a hypergeometric function. $$ \int \frac{x^k}{1-x}dx = \frac{x^{k + 1}\sideset{_2}{_1}F(1, k + 1, k + 2, x)}{k + 1} + C $$ The problem related to summation below: $$ \begin{align} S=&\sum_{n=1}^{\infty}\frac{x^n}{k+n}\quad,k\in[0,2\pi]\\ S=&\sum_{n=1}^{\infty}\frac{x^n}{k+n}\\ x^kS=&\sum_{n=1}^{\infty}\frac{x^{k+n}}{k+n}\\ \frac{d}{dx} (x^kS)=&\sum_{n=1}^{\infty}\frac{(k+n)x^{k+n-1}}{k+n}\quad,\text{if $|x|\lt 1 $}\\ =&\sum_{n=1}^{\infty}x^{k+n-1}=\frac{x^k}{1-x}\\ \int\frac{d}{dx} (x^kS)dx=&\int\frac{x^k}{1-x}dx \end{align} $$
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$$ \int {\frac{{x^k }}{{1 - x}}dx} $$ Let, $1-x = t$. Then, $-dx = dt$. On substituting this, $$ \int\frac{(1-t)^k}{t}(-dt) = \int\frac{1}{t}\sum_{r}\binom{k}{r}(-t)^r(-dt) = -\ln t + \sum_{r}\binom{k}{r}\frac{(-t)^r}{r} . $$
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2As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. – Community Oct 01 '22 at 07:03
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3Note that in the question $k$ is tipically not a positive integer but a real number between $0$ and $2\pi$. – Gary Oct 01 '22 at 07:19
xis in the unit circle as it seems, there are quite simple algorithms to numerically evaluate that Gaussian Hypergeometric function if that's what you're worried about. See my code linked here: https://math.stackexchange.com/a/480175/80812 – horchler Sep 30 '22 at 18:46