The domain of a function f(x) is the set of values of x for which f(x) is real and defined.
For the function f(x) = x^2+2x-3+x+3 , any value of x gives a real value of f(x). As the value of f(x) is real and defined for all values of x, the domain is the set of real numbers.
The domain of the function is the set of real numbers R.
f(x) = x^2+2x-3+x+3.
f(x) for x=0,1,2...(domain)