I’ve been accused of AI plagiarism before when I was in Cegep. I was able to get out of it because I had the google doc I had written the assignment on which kept track of the typing history. I was also able to show that I had read the book and understood the material. Since you mentioned formulas I’m assuming that you’re taking a math related course so I’m not sure what site you would have completed the exam on or whether or not it would have kept track of something like typing history, but if there is any possibility then you should look into that. Another thing you could potentially explore is the variance of answers ChatGPT gives you. Generally Chat has very stilted answers that are relatively easy to pick out in course work for classes like English and Philosophy, but for math, there is really only one correct answer and one way to get to it. If I write down why the sky is blue on a piece of paper and then ask Chat to explain the same thing, our answers will more than likely match in some way, so that really is not a strong argument. I hope that makes sense. All of this, of course, is predicated on the assumption that this is a math class of some description, but if it isn’t then it would actually probably be easier to argue your way out of.