In this lesson, we will learn:
- Expressing Intervals Using a Number Line
 - Expressing Intervals Using Inequalities
 - Expressing Intervals Using Interval Notations
 - Simplifying Multiple Notations
 - Interchanging Between Number Lines, Inequalities and Interval Notations
 
- Interval: all the numbers in between two numbers.
 - Interval notation: a notation for representing an interval as a pair of numbers which are the endpoints of the interval.
 - Intervals can be represented in 3 ways:
- Number line
 - Inequalities (arrows)
 - Interval notations (brackets)
 
 - For a number line, we use a closed circle "•" to represent end points being included and an open circle "°" to represent end points not being included.
 - For inequalities, we use the following symbols:
 - > to denote greater than, above
 - < to denote less than, below
 - ≥ to denote greater than or equal to, at least, no less than, minimum
 - ≤ to denote less than or equal to, at most, no more than, maximum
 - For interval notations, we use a square bracket " [ ] " to represent end points being included and a round bracket or a parenthesis " ( ) " to represent end points not being included.
 - Infinity is not a number, so we can NEVER include it. Hence, we can only use round brackets for infinity.
 - If we want to represent 2 intervals using interval notations, we have to use "∩" to denote "and/intersection" and "∪" to denote "or/union".
 







