\documentclass{article}

\usepackage{geometry}
\usepackage[dutch]{babel}
\usepackage{parskip}
\usepackage{amsmath,amssymb}
\usepackage{graphicx,subcaption}
\usepackage{xcolor}
\usepackage{adjustbox}
\usepackage{booktabs}
\usepackage{tabularx}

\geometry{
	paperwidth=9cm,
	paperheight=7.5cm,
	margin=0.0cm,
    paperheight=4cm
}

\begin{document}

\begin{table}[htbp]
    \centering
    \begin{tabularx}{0.7\textwidth}{X X}
        \toprule
        Formule & Beschrijving\\
        \midrule
        $ \sqrt{2} $ & Wortel\\
        $ \frac{2}{3} $ & Breuk\\
        $ 6\geq 3 $ & Symbool\\
        $ a^2 + b^2 $ & Superscript\\
        \bottomrule
    \end{tabularx}
    \caption{Een tabel!}
\end{table}

\end{document}