我使用rmarkdown和beamer制作教学幻灯片。我试着在幻灯片中插入一个LaTeX方程，这个方程中有一些空格。

$Scott's \space pi = \frac{\% \space obs. \space agreements - \% \space exp. \space agreements}{1 - \% \space exp. \space agreements}$

当我将光标悬停在上面时，Rstudio会正确地预览公式，如您在下面的屏幕截图中所看到的：

然而，当我编织PDF时，空格不会出现，我得到了这个：

我是不是漏掉了什么？
我的markdown header如下：

---
title: "XXXXXXXXXXXXXXXXXXXXXXXXXXXX"
author: "XXXXXXXXXXXXXXXXXXXXXXXXX"
institute: "XXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
date: "XXXXXX"
output:
  beamer_presentation:
    incremental: true
    theme: "Berlin"
    colortheme: "dove"
    fonttheme: "structurebold"
    includes:
      in_header: preamble.tex
classoption: "aspectratio=169"

---

“preamble.tex”文件如下：

\usepackage{caption}
\captionsetup[figure]{labelformat=empty}
\setbeamercolor{frametitle}{fg=white,bg=black} %section slide title
\setbeamercolor{section in foot}{fg=white, bg=black} % footsections
\setbeamercolor{part title}{fg=white, bg=black}
\setbeamertemplate{footline}
{
 \hbox{%
  \begin{beamercolorbox}[wd=.33\paperwidth,ht=2.6ex,dp=1ex,left,leftskip=2ex]{section in foot} % footsection 1
    \usebeamerfont{section in foot}\insertshortauthor
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.33\paperwidth,ht=2.6ex,dp=1ex,center]{section in foot} % footsection 2
    \usebeamerfont{section in foot} \inserttitle
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.34\paperwidth,ht=2.6ex,dp=1ex,right,rightskip=2ex]{section in foot} % footsection 3
    \usebeamerfont{section in foot} XXXXXXXXXXXXXXXXXXXXX
  \end{beamercolorbox}}%

  \vskip0pt%
}

\setbeamertemplate{section page}{
  \centering
  \begin{columns}
  \begin{column}{\paperwidth}
  \begin{beamercolorbox}[sep=12pt,center]{part title}
    \usebeamerfont{section title}\insertsection\par
  \end{beamercolorbox}
  \end{column}
  \end{columns}
}