\documentclass[a4paper, 12pt] {article}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{commath}
\usepackage{dsfont}
\usepackage {geometry}
\geometry{verbose,tmargin=3cm,bmargin=2cm,lmargin=4cm,rmargin=4cm}

\begin{document}
	\begin{equation}
		\hat f(\xi)=\int \limits_{-\infty}^{+\infty} 
		f(x)*e ^{-2 \pi i x \xi} \dif x
	\end{equation}
	

\end{document}