In mathematics, interval notation is a method used to represent a set of numbers on a number line
Closed interval: includes both endpoints ex [-4, 9]
Open interval: does not include either endpoint ex (-5, 12)
Degenerative interval: both endpoints are equal ex [x, x]
Empty interval: contains no elements. Represented by empty set symbol ∅
Mixed interval: one end may include an endpoint, while the other does not. Use parenthesis or square brackets accordingly ex [-3, 14) or (3, 9]
If there is a gap in the interval, they may be joined with a union symbol ∪