It's a single equation taught in high school. I'd expect nearly every adult who'd been through high school to know it or at least have basic familiarity.
I expect you're relatively young. I know what you're talking about but don't remember exactly what it looks like and doubt I could derive it--and probably haven't used it in decades.
I’m not young but HN has an international readership and you have to factor in that for people coming from countries where a heavy focus is put on mathematics the average level in the US is hard to fathom. I learned how to solve quadratic equations during my second year of highschool and by the end of it I could basically do it in my sleep, same things with basic derivation. It’s the same for everyone around me.
The idea that you might not know how to do it as someone working in a STEM related field wouldn’t come to me.
This is not an international difference, everyone coming out of a non-urban public school system will know how to factor a quadratic equation. It is typically taught year 1 of highschool.