Title is a bit confusing, but I'm trying to figure out what's something I should know by heart/know in my head vs. something I don't really need to know but should be able to understand if I refreshed on it.

Something like the circle equation or trig properties - I feel like that's just memorization and not something that people memorize, right? But on the other hand, not knowing how to integrate or differentiate would be a pretty big setback?

I was looking at how to factor polynomials and realized I had forgotten how to do so, but a quick refresher course on Khan and YouTube allowed me to regain the ability.

Or the powers problem here - https://www.reddit.com/r/learnmath/comments/9vap0t/help_with_11_yearolds_maths_homework_needed_yeah/

I also don't know how to do powers, but upon reading the comments it came back to me that it was just adding/subtracting if they have the same base.

I'd feel silly for not knowing how to differentiate/integrate - should I feel silly for not knowing the circle equation/trig/factoring polynomials/powers off the top of my head?

The problem is a lot of this stuff I have never used in real life and was always a purely academic pursuit. After graduating 3 years ago, I've forgotten a lot of specifics.