6.1: Inequality Expressions
Suppose you're having a party, and you know that the number of people attending will be greater than or equal to 25. How would you write this inequality? If you had to graph the solutions to this inequality on a number line, could you do it? After completing this Concept, you'll not only be able to express inequalities such as this one with a graph, but you'll also be able to look at a graph and determine what inequality it represents.
Guidance
Verbs that translate into inequalities are:
Definition: An algebraic inequality is a mathematical sentence connecting an expression to a value, a variable, or another expression with an inequality sign.
Solutions to onevariable inequalities can be graphed on a number line or in a coordinate plane.
Example A
Graph the solutions to
Solution: The inequality is asking for all real numbers larger than 3.
You can also write inequalities given a number line of solutions.
Example B
Write the inequality pictured below.
Solution: The value of four is colored in, meaning that four is a solution to the inequality. The red arrow indicates values less than four. Therefore, the inequality is:
Inequalities that “include” the value are shown as
Four Ways to Express Solutions to Inequalities
1. Inequality notation: The answer is expressed as an algebraic inequality, such as
2. Set notation: The inequality is rewritten using set notation brackets { }. For example,
3. Interval notation: This notation uses brackets to denote the range of values in an inequality.
 Square or “closed” brackets [ ] indicate that the number is included in the solution
 Round or “open” brackets ( ) indicate that the number is not included in the solution.
Interval notation also uses the concept of infinity
4. As a graphed sentence on a number line.
Example C
Describe the set of numbers contained by the given set notation for the following:
a) (8, 24)
b) [3, 12)
Solution:
(8, 24) states that the solution is all numbers between 8 and 24 but does not include the numbers 8 and 24.
[3, 12) states that the solution is all numbers between 3 and 12, including 3 but not including 12.
Guided Practice
Describe and graph the solution set expressed by
Solution:
The solution set contains all numbers less than 3.25, not including 3.25.
The graph on the number line is:
Practice
 What are the four methods of writing the solution to an inequality?
Graph the solutions to the following inequalities using a number line.

x<−3 
x≥6 
x>0 
x≤8 
x<−35 
x>−17 
x≥20 
x≤3
Write the inequality that is represented by each graph.
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Here you'll learn how to express inequalities in various forms, as well as how to graph inequalities on a number line.