\documentclass{article}
\usepackage{amsmath}
\usepackage[utf8]{inputenc}
\begin{document}
\begin{equation}
 \int Cf(x) dx \ = C \int f(x) dx
\end{equation}
\begin{equation}
\int [f(x) \pm g(x)] dx \ = \int f(x) dx \pm \int g(x) dx
\end{equation}
\end{document}