## Interval notation

An Interval notation is a method of writing down a set/range of numbers. We need brackets and a pair of numbers representing two endpoints of a number range. For this we use brackets [] and parentheses () for this. Brackets [ ] mean that the endpoint of the range is included (this is drawn on a number line with a solid dot). Parentheses () mean that the endpoint is excluded and does not contain the listed element (this is drawn on a number line with hollow dot).

So for (−2; 3>, the range starts after −2 (−2 is excluded), but ends with 3 (including 3).

We can write this as:

Or draw:

Infinity symbols ∞ and −∞ are always accompanied by round brackets (). For example, [2, ∞) is the interval of real numbers greater or equal to 2.