My task is to figure out what z is (which can be any number, positive or negative or zero) when I only have access to $x$ and $y$ at any given time.
$x\ge0$.
$\lvert y \rvert <1$.
So, for example, when $x= 150$ and $y=1.0$, I know that $z=30$. When $x=50$ and $y = 0.80$, I've found through experimentation that $z$ is then $10$.
I've collected a few data points and tried to see what kind of relationship they have with another. If this was a $z$ vs $x$ or $z$ vs $y$ thing, I would just toss it onto a scatterplot and see whether its a linear or polynomial or exponential relationship and just find the equation. But I'm not sure what to do when a second variable comes into the equation.
I found this from 5 years ago: How can I determine the best relationship for 3 variables, given several data points?
They seem to be asking what I am asking basically, but I didn't really understand the answers. I was hoping someone could teach me, or at the very least, tell me the "name" of what I am trying to do, so I can look it up myself.