part of square root latex equation dissappears in pdf rendering from RStudio's rmarkdown

Question

When I use this code to make a square root in my pdf document (rendered by rmarkdown):

---
title: "Test"
author: "test test"
geometry: margin=1in
output:
  pdf_document:
    keep_tex: yes
    latex_engine: xelatex
    number_sections: yes
    toc: yes
    toc_depth: 3
  html_document:
    css: tables.css
    number_sections: yes
    theme: cerulean
    toc: yes
    toc_depth: 3
header-includes:
- \usepackage[dutch]{babel}
- \usepackage{fancyhdr}
- \pagestyle{fancy}
- \fancyfoot[LE,RO]{this is a fancy foot}
- \usepackage{dcolumn}
- \usepackage{here}
- \usepackage{longtable}
- \usepackage{caption}
- \captionsetup{skip=2pt,labelsep=space,justification=justified,singlelinecheck=off}
subtitle: test test test
fontsize: 12pt
---

$$ S_E\text{=}S_x\sqrt{\text{(}\text{1}\text{-}r_{xx}\text{)}} $$

this is the result:

Notice the strange looking square root. Does anyone know what's going wrong here in my code?

Answer 1

I found the solution to this problem here:

https://tex.stackexchange.com/questions/210153/pdftex-font-expansion-error-during-compilation

In the directory C:\\Program Files\\MiKTeX 2.9\\miktex\\bin\\x64 I ran updmap.exe. After that the problem was solved.