\documentclass[a5paper]{article}
\usepackage[margin=5mm]{geometry}
\usepackage{amsmath}
\usepackage{tkz-interval}
\setKVdefault[tkzinterv]{left color=teal,right color=red}
\def\IntervtestA{-4;\dfrac{1}{7}}
\def\IntervtestB{\dfrac{1}{2};\sqrt{7}}
\begin{document}
%with tkz-interval package
$x \in \tkzinterval{\IntervtestA} \cup \tkzinterval[open]{\IntervtestB}$
$x \in \tkzinterval[open]{\IntervtestA} \cup \tkzinterval[open]{\IntervtestB}$
$x \in \tkzinterval[open right]{\IntervtestA} \cup \tkzinterval[open]{\IntervtestB}$
$x \in \tkzinterval[open left]{\IntervtestA} \cup \tkzinterval[open]{\IntervtestB}$.
\end{document}