Make R Markdown code blocks into math mode - r-markdown

Question

I would love to use R Markdown to generate homework and exam solutions, but I would prefer to have them more readable to non-coders.
I there a way that I can pass the ECHO output through math mode? That is I would love to have an ECHO that looks more "inline" and less like code. I can see how to hide it, but in the R Markdown Reference Guide I don't see an option to remove the "code block" and wrap each line in $$ (or wrap in anything). Is there a way to do this?
Here is an example. This solution has all the meat, but may be a little intimdating to some students (this is not an R course).
8-22 ...
a. ...
```{r part_a}
D_0 = 2.40
g = 0.06
r = 0.12
V = D_0*(1 + g)/(r - g)
V
```
Instead, I would love to see something more like the following.^[I appreciate that I can generate this output with some cutting and pasting and a text editor, I am just trying to find the most efficient solution, since this is likely something that I will do more than once or twice.]
8.22 ...
a. ...
$$ D_0 = 2.40 $$
$$ g = 0.06 $$
$$ r = 0.12 $$
$$ V = D_0 \times (1 + g)/(r - g) = 2.40 \times (1 + 0.06)/(0.12 - 0.06) = `r V`$$

Answer 1

I have a partial answer. I don't yet know how to replace variable x with its value so that a can print the formula with variables, replaced by numbers. But I can generate the "math code" block so that I can solve the problem and generate the pretty solution without a lot of cut and paste.
Here is an example .Rmd file.
---
author: Richard Herron
title: Homework Solutions
---
8-22 ...
a. ...
There are three parts to this solution.
1. write the equations to solve the problem in R-readable strings.
2. loop over the list and `eval(parse())` the equation strings
3. wrap strings in `$$ $$` with `cat(paste0())`
Chunks should be set to `echo=FALSE` and `results="asis`. You may need to suppress some function output with `invisible()`.
```{r part_a, echo=FALSE, results="asis"}
# just to make sure my eval below works
rm(list=ls())
# store solution as a list of character equations
solution <- list(
"D_0 = 2.40",
"g = 0.06",
"r = 0.12",
"V = D_0*(1 + g)/(r - g)"
)
# "solve" problem
for (i in seq_along(solution)) eval(parse(text=solution[[i]]))
# display solution as math
cat(paste0("$$", solution, "$$"), sep="\n")
```
Because of the `eval()` loop in the first chunk I can say that $V = `r V`$ in the text that follows.
And here is an outer file that convert each .Rmd file into a .pdf.
# load `render` and set working directory
setwd("C:/Users/Richard/Dropbox/Babson College/SME 2021 for 2015 fall/Homework")
# loop over all Rmd files
require(rmarkdown)
require(tools)
files <- list.files(path=".", pattern="*.Rmd")
roots <- sapply(files, file_path_sans_ext)
namesIn <- paste0("", roots, ".pdf")
namesOut <- paste0("", roots, ".pdf")
# solutions
myPdf <- pdf_document(
fig_caption=TRUE,
keep_tex=TRUE,
pandoc_args=c(
"--variable=classoption:fleqn",
"--variable=classoption:twocolumn",
paste0("--metadata=date:", format(Sys.time(), "%B %d, %Y"))
)
)
lapply(files, FUN=render, output_format=myPdf)
mapply(file.rename, namesIn, namesOut)
Which yields this pdf.