Hi, welcome to Math SE! Can you show us the proof you’re looking at? There are a lot of false proofs of this sort out there, typically involving division by 0, I would imagine that’s probably the gimmick in the proof you’ve found. Here’s a helpful link to get a sense for how to use MathJax.
https://math.stackexchange.com/questions/4010453/how-can-11-3-be-possible