>Is factoring a quadratic equation supposed to be some example of some obscure math principle that is useless?

I've been a successful software engineer for over ten years, yet without looking it up, I don't even know what "factoring a quadratic equation" means, let alone how to do it.

It's from high school algebra, it's a specific instance of "factoring" where the equation has the form: ax^2+bx+c=0 and you want (x+r_1)(x+r_2)=0. "factoring" is the general process of finding what things multiply together to produce a term. Which is where we, in software, get the notions of "factoring" (described well in the context of Forth with Thinking Forth or Starting Forth, can't remember which, maybe both) and "refactoring".

Code refactoring and factoring in algebra are related in the sense that they aren't meant to change the system (that is, its meaning or behavior), but instead are meant to change its appearance. In particular, in the above, if you can factor it out you end up with the two roots (what I termed r_1 and r_2) of the equation, which are useful for various other things.

> "factoring a quadratic equation"

This is hard to understand because it doesn't make sense. Quadratic polynomials (or more generally, algebraic expressions) are factored. Equations are not factored.

?

x^2 + 2x - 3 = 0 = (x+3)(x-1)

This is not factoring?

It's something you learn in middle school or high school math. Pretty good bet that a college freshman would be familiar with it.

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.

And those of us who may not have done it in multiple decades may just not remember.