I am reading a research paper. If you look at equation $(2.7)$ in the pdf , the authors write a Fourier cosine series as an Abels integral:
$$\begin{align}\frac{a_0}2+\sum_{n=1}^{\infty}a_n\cos(n\theta)~=~\cos\frac12\theta\int_{\theta}^{\pi-\varepsilon}\frac{h_1(t)dt}{\sqrt{\cos\theta-\cos t}}\tag{2.7}\end{align}$$
Does anyone know a reference for such a representation. Where can I read more about this?
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