# Homework Help: Quick question about domain

1. Feb 18, 2008

### Incog

1. The problem statement, all variables and given/known data

I have to do a few graphs and some equations with certain domains but I've never seen the domain written in this way:

Usually I see the domain written with something like 2<x<4. What exactly does the above mean?

2. Feb 18, 2008

### cristo

Staff Emeritus
$x\in (-\infty,2]$ means $-\infty<x\leq 2$ and $x\in(2,\infty)$ means $2<x<\infty$

3. Feb 18, 2008

### astrosona

2+ means go to near 2 from the right side (from number greater than 2) and 2- means go to near 2 from number less than 2 which means the left side

OK, now in here when you want to find the limit of the function because you have a discontinued in 2 (the value of your function is different in left and right of 2) the limit is different wile you look it from left of 2 or right of 2,

the key point is try to find the limit of f from 2+ from the function that is valid in (2,oo) and try to find the limit of f from 2- from the function that is valid in (-oo, 2]