RemNote supports the inclusion of mathematical equations using LaTeX syntax (specifically, the KaTeX mathematical typesetting system for the web).
Adding equations in RemNote
To enter an equation in LaTeX, type
$$ in any Rem. A popup will appear and allow you to edit the LaTeX markup; the resulting equation will be displayed as a preview in your notes. When you have the equation right, click Done or press Enter.
After you've created an equation, click on it or move the cursor over it with the arrow keys to reopen the popup to edit it.
If you have a larger equation, you can change it from Inline to Block mode to place it on its own line by selecting the appropriate option from the drop-down or pressing Alt+B:
Here are a few more complicated equations to give you an idea of what's possible:
Finding the right LaTeX markup
LaTeX is a highly efficient way of entering equations once you're familiar with it, but if you've never used it before, the necessary markup codes are not obvious. The Supported Functions section of the KaTeX website provides a great reference, and you can click the ? icon in the upper-right corner of the popup at any time to go there.
Another useful resource is Detexify, which allows you to sketch a symbol you're trying to reproduce and see a list of similar symbols known to LaTeX.
Note that not all symbols found in Detexify are supported in KaTeX. The Supported Functions table above is the definitive reference.