## Interval notation

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. We use for this brackets [] and parentheses () for this. Brackets [ ] mean that the endpoint of the range is included (this is drawn on a number line with a full dot). Parentheses () mean that the endpoint is excluded and doesn't contain the listed element (this is drawn on a number line with empty dot). So for [0, 10), the range starts with 0 (and includes it), but ends just before 10 (excluding 10).

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