[Tex/LaTex] How to write relative permittivity in text

Question

I'd like to use these two symbols in the text of my thesis. How would I write them?

&

Answer 1

LaTeX provides, as any new user finds out, support for greek letters in math mode, with macro names that are spelled out: \alpha, \beta, \delta, etc.

Unfortunately, the default appearance of \epsilon is

which is not what the OP was seeking.

However, one finds on p.43 of Lamport's LaTeX User Guide that several greek letters have variants that are available through standard LaTeX. Namely, \varepsilon, \vartheta, \varpi, \varsigma, \varphi.

A comparison of the standard versus the variant forms is given below:

We find that, indeed, \varepsilon is the desired form of the OP.

Other details about the OP's question were the inclusion of subscripts These are done in math mode, with the subscript following a _ character; however, only a single character is typically absorbed into the subscript (e.g., \varepsilon_0), so that longer subscripts should be grouped in braces as \varepsilon_{xy}. In the case of one of the OP's examples, an upright r was requested as the subscript. If one used \varepsilon_r, the r would be in standard math mode, which is italic

However, one can ask for upright math mode by way of \mathrm{} (math-roman), which already comes pre-grouped, so that \varepsilon_\mathrm{r} yields

The only final thing to mention, which is very introductory, is that inline math (so-called \textstyle) is accessed by way of dollar delimiters $...$, or in many ways more preferably, \(...\) delimiters. If one wants the math on a line by itself (so-called \displaystyle), with no efforts to compress the expression into a single row height, then \[...\] delimiters are used, or else one of the many LaTeX math environments such as equation or the amsmath.sty environments in the align family.

Thus, to achieve the OP's request, I provide the following MWE:

\documentclass{article}
\begin{document}
$\varepsilon_\mathrm{r}$ and $\varepsilon_0$ are inline expressions
\end{document}