# Function help: How to know if domain is all real numbers

#### ECD Hollis

##### New member
In a graph, how do I know if the domain is the set of all real numbers?

#### Subhotosh Khan

##### Super Moderator
Staff member
When at every value of x (in real domain) the function is defined.

For example

f(x) = x^2

in here the function is defined et every value of 'x'.

another case

f(x) = x/{(x-2)(x-3)}

here at x=2 and x=3 , the function is not defined (division by zero). Hence the domain is all real x, except x=2 and x=3.

In a graph, around these points, the value of y will go to ±infinity.

Another example

y = (x)^(1/2)

Here when x<0, the function is undefined (complex) in real range. So the domain of the function is x ≥ 0. For this one - the graph simply does not exist in the negative domain.

#### wjm11

##### Senior Member
In a graph, how do I know if the domain is the set of all real numbers?
To add to Subhotosh's comments,
What is the definition of domain? It will be helpful to you to look it up.

Here’s the idea in a nutshell: it’s the allowable x values. For any points on a graph, the domain consists of the x values of those points.

All lines except vertical lines, for example, have domains that are all real numbers.

#### ECD Hollis

##### New member
Thanks guys. Man I am not cut out for this math stuff. I want to magor in Political Science in college, so you could imagine, I'm not very good with numbers.

I'm trying my best to pass this course.

#### Subhotosh Khan

##### Super Moderator
Staff member
ECD Hollis said:
I want to magor in Political Science in college, ..... I'm not very good with numbers
You would need to understand poll-statistics - otherwise you won't be able to change your "stance" fast enough.....

#### ECD Hollis

##### New member
Subhotosh Khan said:
[quote="ECD Hollis":1aymvmml] I want to magor in Political Science in college, ..... I'm not very good with numbers
You would need to understand poll-statistics - otherwise you won't be able to change your "stance" fast enough.....[/quote:1aymvmml]

Stance? Oh, I think I get you.

#### pka

##### Elite Member
ECD Hollis said:
Man I am not cut out for this math stuff. I want to magor in Political Science in college, so you could imagine, I'm not very good with numbers.
Any decent program in political science program today contains a good bit of mathematics. Along with probability and statistics, game theory is important component of graduate study as well as rational decision theory.

#### ECD Hollis

##### New member
pka said:
ECD Hollis said:
Man I am not cut out for this math stuff. I want to magor in Political Science in college, so you could imagine, I'm not very good with numbers.
Any decent program in political science program today contains a good bit of mathematics. Along with probability and statistics, game theory is important component of graduate study as well as rational decision theory.
Probability and Statistics is an area I think I will do okay in. It's Algebra and Advanced Mathematics that gives me a hard time. It's like my mind doesn't work like that.