\documentclass[12pt]{amsart}
\parindent=0pt \parskip=8pt

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\begin{document}

$$
	c_n = \int_{-\pi}^\pi e^{-inx} f(x) dx
$$

$$
	\tilde{f}_N(x) = \sum_{n=-N}^{N} c_n e^{inx}
$$

\end{document}
