>Where are you that high school only covers up to precalculus? In Australia (depending on the level) you do multivariate calculus among other things. Perhaps other subjects aren't covered as deeply.

I'm from the US. The state of mathematics education here is absolutely embarrassing to pretty much any other developed country. Taking precalculus is actually considered advanced, most students graduate with nothing more than an "Algebra" class that covers basic algebraic notation, quadratic equations, linear equations, and not much beyond that. Calculus 1 (single variable) is considered an advanced math class that is only taken by STEM majors for freshman university students here.