Formula in a variable that can be referenced later

Is there a way to put a formula in a variable (as in like a programming language variable) so that it can be referred to and rendered later? I was able to do this in Mathematica, but I’m moving away from Mathematica because I don’t want to pay for it. I want to change to something more openly available like LaTex for displaying math formulas.

Note: I’m using Jupyter Notebook, which happens to use MathJax for LaTex rendering.

Though I mentioned programming language variables, Mathematica, and Jupyter Notebook, I am asking about doing this purely in LaTex (MathJax in my case).

I didn’t have a lot of time with Mathematica, but here’s an example of something that could be done in Mathematica

some_function = a/b
x = some_function/c
Display[x];

The result would be something like this:

documentclass{standalone}

newcommand{somefunction}{frac{a}{b}}
newcommand{x}{frac{somefunction}{c}}

begin{document}
    $x$
end{document}