which is the domain of the function f(x) =
Domain and Range. When we look at a function like f(x) = x + 2, we can easily say where the function f(x), in this case, the value along the y-axis, is at any point we choose along the x-axis. We know that at x = 3.4, f(x) = 5.4. The values of x that the function will output a value for is called the domain of f. In the case of f(x) = x + 2, the domain is the entire x-axis, or, formally speaking, all real numbers. The values which f(x) takes on is called the range of f.