Inverse function of function with 2 variables.

Maybe this question has possible duplicate or something, but i still don't get it.

Suppose i have this function :

$$f(x,y)=x+y$$

What is the inverse of this? Is it possible? Bcz, i'm not learning the inverse of multivariable function on calculus.

Assume that your function is $$f:\mathbb R^2 \to \mathbb R$$ Since $$f(1,-1)=f(2,-2)=0$$ your function is not injective and therefore it does not have an inverse.