how to get a percent sign when spinning with latex or html

percent_sign_latex_html.rmd

---
title: TEST
output:
    pdf_document:
        latex_engine: xelatex
    html_document:
        fig_caption: true
---

```{r, echo = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  echo = TRUE,
  cache = FALSE,
  comment = "#>",
  fig.path = "fig-",
  fig.pos = "h"
)

# this will check what the output format is going to be
getOutputFormat <- function() {
  knitr::opts_knit$get("rmarkdown.pandoc.to")
}
```


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```{r, warning=FALSE, message=FALSE, echo=FALSE, eval=TRUE, results='asis'}
s <- "$$\\text{\\% change} = \\frac{x_2 - x_1}{x_1} \\times 100$$"
if(getOutputFormat() == 'html') s <- gsub('\\\\%', '%', s) # dont escape if html
knitr::asis_output(s)
```

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