For instance I asked chatGPT to write a code for square root which it did using inbuilt Math.sqrt function. I instructed it to write without using inbuilt function which it did. However, no matter how many times I instructed it to avoid using Math.floor or Math.ceil, it was not taking any heed.
It's also very good at tedious complicated maths. While using it for hobby gamedev it's been super great for writing code for transformations, animations, rotations in 3d space etc. While those are things I could do given maybe 20 mins, it can often get them first or second try (under a minute!)
It's not a superhero, and having watched people with no experience using it, its not nearly as helpful if you have no idea what you're doing, but it has a real sweet spot when you are generally experienced but new to a technology, field or project