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# Sign of a Number

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.
or
x>0
Negative Numbers A real number x is said to be negative if it is less than 0.
or
x<0
Non-Positive Numbers A real number x is said to be non-positive if it is less than or equal to 0.
or
x0
Non-Negative Numbers A real number x is said to be non-negative if it is greater than or equal to 0.
or
x0
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.
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