箭头指向等式中的等号以证明其正确性

Question

我的问题很简单：可以做到这一点吗？

我只想知道这是否可行以及如何实现。箭头颜色无关紧要。当然，我在另一个应用程序中做过这个，文本属于 LaTeX，但箭头不属于。

Answer 1

\mathclap这是一个使用包的宏mathtools和包\substack的宏的解决方案amsmath。（附言：包会自动mathtools加载包。）amsmath

\documentclass{article} % or some other suitable docuemnt class
\usepackage{mathtools,xcolor}
% \usepackage{graphicx} % optional, for \rotatebox macro

\begin{document}
\[
a+b\underset{\substack{\color{red}\uparrow \\ % or: \rotatebox{90}{$\longrightarrow$}
                       \mathclap{\textup{\tiny commutative}} \\  
                       \mathclap{\textup{\tiny property}}}}{=}b+a
\]
\end{document}

Answer 2

一个使用库的示例tikzmark，正​​如我在上面的评论中提到的：

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows.meta,
                tikzmark}

\usepackage{lipsum}

\begin{document}
\lipsum[66]
\[
a + b 
    \tikzmarknode[inner xsep=3pt]{A}{ = }
        b + a
\begin{tikzpicture}[overlay, remember picture, shorten <=1mm,
                    nodes={font=\small, text=black, align=center}]
\draw[thick, red, Straight Barb-] (A.south) -- ++ (0,-1) node[below] {commutative\\ property};
\end{tikzpicture}
\vspace{17mm}
\]
\lipsum[66]
\end{document}

经过三次编译结果是：

Answer 3

和https://www.mathcha.io/editor做法很简单。这里有一个例子。

\documentclass[a4paper,12pt]{article}
\usepackage{tikz}


\begin{document}
\tikzset{every picture/.style={line width=0.75pt}} 
\begin{tikzpicture}[x=0.75pt,y=0.75pt,yscale=-1,xscale=1]
\draw [color={rgb, 255:red, 208; green, 2; blue, 27 }  ,draw opacity=1 ]   (192,108) -- (192,66) ;
\draw [shift={(192,64)}, rotate = 90] [color={rgb, 255:red, 208; green, 2; blue, 27 }  ,draw opacity=1 ][line width=0.75]    (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29)   ;
\draw (192,53) node  [color={rgb, 255:red, 0; green, 0; blue, 0 }  ,opacity=1 ]  {$a+b=b+a$};
\draw (121,108) node [anchor=north west][inner sep=0.75pt]   [align=left] {commutative property};
\end{tikzpicture}

\end{document}