如何在方程式下画箭头？

Question

我不知道如何制作红色圈出的箭头：

以下是我目前所掌握的信息：

\dfrac{5}{6} \div \left(-\dfrac{3}{4}\right)=\dfrac{5}{6} \times \left(-\dfrac{4}{3}\right)=-\dfac{10}{9}

Answer 1

通过使用tikzmarknode？

\documentclass{article}
\usepackage{mathtools}
\usepackage{tikz}
\usetikzlibrary{tikzmark}

\usepackage{lipsum}

\begin{document}
\[
\dfrac{5}{6} \tikzmarknode{a}{\div \left(-\dfrac{3}{4}\right)}
    = \dfrac{5}{6} \tikzmarknode{b}{\times \left(-\dfrac{4}{3}\right)}
    = -\dfrac{10}{9}
%
    \begin{tikzpicture}[
overlay,remember picture,
transform canvas={yshift=-2pt}, cyan
                        ]
\draw [->] (a.south) -- ++ (0,-2mm) -| (b) node[pos=0.25, below] {text};
\draw   (a.south west) -- (a.south east)
        (b.south west) -- (b.south east);
    \end{tikzpicture}
\vspace{1.5\baselineskip}   % reserves space for the image
\]
\lipsum[66]
\end{document}

经过两次编译你将得到：