How to deal with this math processing errors?

I tried to refresh or to run again but it is the same

Looks like an inability to interpret a statement in the math markup language https://en.m.wikipedia.org/wiki/Mathematical_markup_language. You could try loading the notebook in a different browser or browser version. Or try view source to see the script.

Yes, as *ai_curious* says, it looks like a rendering problem in your browser. I’ve seen this sometimes on Discourse posts also, but usually a “Refresh” is enough to restore order. One thing to check is your browser config: perhaps you’ve got restrictive settings about what “plugins” are allowed. The LaTeX rendering is handled by the MathJax plugin at least in Chrome and FireFox.

Actually, we can run a little experiment right here:

sin^2x + cos^2x = 1

That’s a LaTeX expression using the Discourse syntax of bracketing it with single dollar signs. Does that give you the “math processing error” again or do you see the familiar sine squared x plus cosine squared x equals 1 formula from trigonometry? If that renders correctly for you, then it’s not a plugin problem.