or

$$\sqrt{2}$$

or maybe

`math f(x) = \int_{-\infty}^\infty\hat f(\xi),e^{2 \pi i \xi x},d\xi `

should render using MathJax.

(If it's a choice, I would prefer the dollar sign markup, since it's used on other sites.)

I don't know anything about nodeBB, but maybe these are what it needs?

https://github.com/benabel/nodebb-plugin-katex

https://www.npmjs.com/package/nodebb-plugin-math

https://community.nodebb.org/topic/8278/mathjax-support/15?_=1613103140024&lang=en-US

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