{{ item.displayTitle }}

No history yet!

Student

Teacher

{{ item.displayTitle }}

{{ item.subject.displayTitle }}

{{ searchError }}

{{ courseTrack.displayTitle }} {{ statistics.percent }}% Sign in to view progress

{{ printedBook.courseTrack.name }} {{ printedBook.name }} 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.

A real number $n$ is said to be **positive** if it is *greater than* $0.$
$0<n<∞ $

Sets of numbers that are **non-negative** can include not only positive numbers but also $0.$
$0≤n<∞ $

**Negative** numbers are the opposite of positive numbers; a real number $n$ is said to be negative if it is *less than* $0.$ Adding a positive number and its corresponding negative will result in a sum of $0.$
$-∞<n<0 $

Similar to non-negative numbers, a set of numbers that are **non-positive** can include both negative numbers and $0.$
$-∞<n≤0 $

Notice how the point at $0$ is closed when it is included in the set and open when it is not.