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An interval on a number line, consisting of the real numbers, contains an infinite amount of numbers. In the interval $1≤x≤4$, all numbers between the $x-$values $1$ and $4$ are a part of the set. For example, $1$, $2.7$, $3.5$, $3.61$ and $4$. An interval does not have to be limited between two ends. For example, the inequality $x≥0$ is a set of *all* positive real numbers larger than or equal to 0.

Interval notation is a way to denote an interval. In this notation, a square bracket $[]$ is used when the end value is *included* and a round bracket $()$ is used when the end value is *not* *included*.

$-1≤x<2 $

The inequality can be translated to interval notation where $[$ indicates that the end point is included and $)$ that it is not.
$[-1,2) $

The interval can then be read as all numbers greater and equal to $-1$ and less than $2$.More examples of intervals are provided below with interval notation along with number line and inequality representations.

Note that if the variable only has one limit, the other is infinity and is