In a calculated question I used {R} to define a placeholder value. Now, in some circumstances, I would like to write just the character "R" as simple character without getting it substituted by nummerical values. But when I want to write the character "R" as a denominator in a fraction, I get a problem:
In the mathjax code
$$\begin{aligned}\varphi_{Z}=\arctan\,\left(\frac{2\cdot\pi\cdot50\,Hz\cdot10^{-3}\cdot L}{R} \right)\end{aligned}$$
the "R" as a denominator gets has to be in curly brackets and now gets interpreted as placeholder.
When I try to "escape" with \text, the same thing happens:
$$\begin{aligned}\varphi_{Z}=\arctan\,\left(\frac{2\cdot\pi\cdot50\,Hz\cdot10^{-3}\cdot L}{\text{R}} \right)\end{aligned}$$How can I just have it rendered as character? I know, I could use a different name for the placeholder like {Rplaceholder} but unfortunately this isn't possible in my usecase.
Hope someone has a solution.