LaTeX \cong not rendering

[mrkitz]

Noob here.

In my gmail $\triangle ABC \cong \triangle XYZ$ gives error [\cong?] while replacing \cong with \sim, \neq, \approx, or \simeq, etc all render just fine.

[adam-p]

For TeX rendering, you're at the mercy of the service being used (yes, I just passed the buck). By default, the service is Google's (deprecated) Image Charts API, described here: https://developers.google.com/chart/infographics/docs/formulas

I don't know of a complete list of math symbols it supports, but it's clearly not all of them, and clearly not \cong.

But you can use a different rendering service. The wiki describes how to use CodeCogs for SVG rendering. Make sure to read that to understand the privacy implications.

However... you can't use SVG in email (it'll get stripped out). But you can use CodeCog's PNG renderer. In the Markdown Here options page, in the "TeX Mathematical Formulae Support" section, replace the default value with this:

<img src="https://latex.codecogs.com/png.latex?{urlmathcode}" alt="{mathcode}">

Now \cong will render.

(I'm going to update the wiki with this info.)