Question

how do i know when the domain is all reall numbers or (-infinity, infinity)

Answer 1

isn't that the same thing ?
what's the difference?

Answer 2

it is the same thing im asking how can i tell when the Domain is all real numbers? such as EX: f(x) = 9-x^2

Answer 3

^^^ i know the answer is all real numbers but i am asking how do i tell?

Answer 4

There is nothing that "goes" bad for any x with f(x)=9-x^2

Answer 5

If u r asking whether there is a formula for telling u the domain, there isn't.

Answer 6

So for instance, with sqrt you just have to know that it is 0 or +

Answer 7

So, at the end, as fiddlearound says, if there is no obvious reason why it is isn't R, then it is R.

Answer 8

soo for the same problem i gave the range would then be what?

cause you solve for x to get the range right?

Answer 9

You can always choose R to be the codomain of a real function.,

Answer 10

mmk thanks