I've encountered an integral that has piqued my interest and am seeking insights or methods for its evaluation. The integral in question is:
$$
\int_{0}^{2\pi} \ln(s^2x^2 + 1) \, ds
$$
where ($x$) is treated as a constant parameter. This integral arises in a specific context I'm studying, and I'm particularly interested in understanding how its value changes with different values of ($x$).
Despite my efforts, I've found that this integral does not yield easily to standard techniques or elementary functions for its antiderivative. Numerical methods and special functions seem to be viable paths, but I'm curious about any analytic approaches or insights the community might have.
Figure Description
Attached is a plot showing how the value of the integral changes as a function of ($x$) over the range from -2 to 2. The plot illustrates the integral's sensitivity to changes in ($x$) and provides a visual representation of the problem at hand.
I'm looking for any of the following:
- Analytic approaches to tackle this integral.
- Insights into the behavior of this integral with respect to ($x$).
- References to similar integrals or relevant mathematical literature.
Thank you in advance for your time and assistance!
Best Answer
Integrate by parts
\begin{align} &\int_{0}^{2\pi} \ln(s^2x^2 + 1)ds\\ =& \ 2\pi\ln(4\pi^2 x^2+1) - \int_{0}^{2\pi} \frac{2s^2 x^2}{s^2 x^2 + 1}ds\\ =&\ 2\pi\ln(4\pi^2 x^2+1) +\frac{2\tan^{-1}(2\pi x)}x-4\pi \end{align}