Sign In
Part of the description of any real number is its sign — it can be positive, negative, or zero. When discussing a set of numbers, it can sometimes be helpful to know how to describe the sign of all numbers within the set.
| Definition | Representation | |
|---|---|---|
| Positive Numbers | A real number x is said to be positive if it is greater than 0. | 0 x>0 |
| Negative Numbers | A real number x is said to be negative if it is less than 0. | - ∞ x<0 |
| Non-Positive Numbers | A real number x is said to be non-positive if it is less than or equal to 0. | - ∞ x≤ 0 |
| Non-Negative Numbers | A real number x is said to be non-negative if it is greater than or equal to 0. | 0≤ x<∞ or x≥ 0 |
Each of these sets of numbers — positive, negative, non-positive, and non-negative — can be represented on a number line.
The point at 0 is closed when it is included in the set and open when it is not.