I like this little tidbit (minus the negative geometry piece of course.) I’ll add that you could use this as an example of something bigger. I don’t think I would have this be a standalone thing.
I know you said math isn’t your thing, but this could still be an example of some other bigger trait/EC/thing.
For example, maybe one of your essays is about you always “going above and beyond” and this could be one example of that.
Or maybe an essay is about your insatiable curiosity – this could be brought up as an example of that.
Or, maybe your essay is about giving back, well this could work in as an example.
So I guess I would say, maybe not worth a mention all on its own, but it would be a great thing to layer in and give depth to your profile in some way.
Another way to look at it: why did you create this study guide, given you don’t like math? Whatever that reason is – it’s probably reflected somewhere in your application, so think about using this as “proof” for that assertion.
That said, this is a “nice to have” tidbit. Don’t force it if you can’t find a home for it. But it’s a nice little example that shows who you are.
HTH.