Question

What is the domain of `f(x) = x`?

Answer 1

All real values of `x`.

The "domain" of a function is the set of values that you can put into the function such that the function is defined. It's easiest to understand this in terms of a counter-example. For instance, `x=0` is NOT part of the domain of `y=1/x`, because when you put that value into the function, the function isn't defined (i.e. `1/0` isn't defined).

For the function `f(x)=x`, you can put any real value of `x` into `f(x)` and it will be defined - so that means the domain of this function is all real values of `x`.