1. Exam 3 Material Inequalities and Absolute Value
Intermediate Algebra
Exam 3 Material
Inequalities and Absolute Value

2. Inequalities
An equation is a comparison that says two algebraic expressions are equal
An inequality is a comparison between two or three algebraic expressions using symbols for:
greater than:
greater than or equal to:
less than:
less than or equal to:
Examples: .

3. Inequalities
There are lots of different types of inequalities, and each is solved in a special way
Inequalities are called equivalent if they have exactly the same solutions
Equivalent inequalities are obtained by using “properties of inequalities”

4. Properties of Inequalities
Adding or subtracting the same number to all parts of an inequality gives an equivalent inequality with the same sense (direction) of the inequality symbol
Multiplying or dividing all parts of an inequality by the same POSITIVE number gives an equivalent inequality with the same sense (direction) of the inequality symbol
Multiplying or dividing all parts of an inequality by the same NEGATIVE number and changing the sense (direction) of the inequality symbol gives an equivalent inequality

5. Solutions to Inequalities
Whereas solutions to equations are usually sets of individual numbers, solutions to inequalities are typically intervals of numbers
Example:
Solution to x = 3 is {3}
Solution to x < 3 is every real number that is less than three
Solutions to inequalities may be expressed in:
Standard Notation
Graphical Notation
Interval Notation

6. Two Part Linear Inequalities
A two part linear inequality is one that looks the same as a linear equation except that an equal sign is replaced by inequality symbol (greater than, greater than or equal to, less than, or less than or equal to)
Example:

7. Expressing Solutions to Two Part Inequalities
“Standard notation” - variable appears alone on left side of inequality symbol, and a number appears alone on right side:
“Graphical notation” - solutions are shaded on a number line using arrows to indicate all numbers to left or right of where shading ends, and using a parenthesis to indicate that a number is not included, and a square bracket to indicate that a number is included
“Interval notation” - solutions are indicated by listing in order the smallest and largest numbers that are in the solution interval, separated by comma, enclosed within parenthesis and/or square bracket. If there is no limit in the negative direction, “negative infinity symbol” is used, and if there is no limit in the positive direction, a “positive infinity symbol” is used. When infinity symbols are used, they are always used with a parenthesis.

8. Solving Two Part Linear Inequalities
Solve exactly like linear equations EXCEPT:
Always isolate variable on left side of inequality
Correctly apply principles of inequalities
(In particular, always remember to reverse sense of inequality when multiplying or dividing by a negative)

9. Example of Solving Two Part Linear Inequalities

10. Three Part Linear Inequalities
Consist of three algebraic expressions compared with two inequality symbols
Both inequality symbols MUST have the same sense (point the same direction) AND must make a true statement when the middle expression is ignored
Good Example:
Not Legitimate: .

11. Expressing Solutions to Three Part Inequalities
“Standard notation” - variable appears alone in the middle part of the three expressions being compared with two inequality symbols:
“Graphical notation” – same as with two part inequalities:
“Interval notation” – same as with two part inequalities:

12. Solving Three Part Linear Inequalities
Solved exactly like two part linear inequalities except that solution is achieved when variable is isolated in the middle

13. Example of Solving Three Part Linear Inequalities

14. Homework Problems Section: 2.8 Page: 174
Problems: Odd: 3 – 17, 21 – 25, – 71
MyMathLab Homework Assignment 2.8 for practice
MyMathLab Quiz 2.8 for grade

15. Sets A “set” is a collection of objects (elements)
In mathematics we often deal with sets whose elements are numbers
Sets of numbers can be expressed in a variety of ways:

16. Empty Set A set that contains no elements is called the “empty set”
The two traditional ways of indicating the empty set are:

17. Intersection of Sets
The intersection of two sets is a new set that contains only those elements that are found in both the first AND and second set
The intersection of sets and is indicated by
Given and

18. Union of Sets
The union of two sets is a new set that contains all those elements that are found either in the first OR the second set
The intersection of sets and is indicated by
Given and

19. Intersection and Union Examples
Given and
Find the intersection and then the union (it may help to first graph each set on a number line)
Find

20. Compound Inequalities
A compound inequality consists of two inequalities joined by the word “AND” or by the word “OR”
Examples:

21. Solving Compound Inequalities Involving “AND”
To solve a compound inequality that uses the connective word “AND” we solve each inequality separately and then intersect the solution sets
Example:

22. Solving Compound Inequalities Involving “OR”
To solve a compound inequality that uses the connective word “OR” we solve each inequality separately and then union the solution sets
Example:

23. Homework Problems Section: 9.1 Page: 626 Problems: Odd: 7 – 61
MyMathLab Homework Assignment 9.1 for practice
MyMathLab Quiz 9.1 for grade

24. Definition of Absolute Value
“Absolute value” means “distance away from zero” on a number line
Distance is always positive or zero
Absolute value is indicated by placing vertical parallel bars on either side of a number or expression
Examples:
The distance away from zero of -3 is shown as:
The distance away from zero of 3 is shown as:
The distance away from zero of u is shown as:

25. Absolute Value Equation
An equation that has a variable contained within absolute value symbols
Examples:
| 2x – 3 | + 6 = 11
| x – 8 | – | 7x + 4 | = 0
| 3x | + 4 = 0

26. Solving Absolute Value Equations
Isolate one absolute value that contains an algebraic expression, | u |
If the other side is negative there is no solution (distance can’t be negative)
If the other side is zero, then write:
u = 0 and Solve
If the other side is “positive n”, then write:
u = n OR u = - n and Solve
If the other side is another absolute value expression, | v |, then write:
u = v OR u = - v and Solve

27. Example of Solving Absolute Value Equation

28. Example of Solving Absolute Value Equation

29. Example of Solving Absolute Value Equation

30. Absolute Value Inequality
Looks like an absolute value equation EXCEPT that an equal sign is replaced by one of the inequality symbols
Examples:
| 3x | – 6 > 0
| 2x – 1 | + 4 < 9
| 5x - 3 | < -7

31. Solving Absolute Value Inequalities
Isolate the absolute value on the left side to write the inequality in one of the forms:
| u | < n or | u | > n
2a. If | u | < n, then write and solve one of these:
u > -n AND u < n (Compound Inequality)
-n < u < n (Three part inequality)
2b. If | u | > n, then write and solve:
u < -n OR u > n (Compound inequality)
3. Write answer in interval notation

32. Example: Solve: | 3x | – 6 > 0
1. Isolate the absolute value on the left side to write the inequality in one of the forms:
| u | < n or | u | > n
2a. If | u | < n, then write:
-n < u < n , and solve
2b. If | u | > n, then write:
u < -n OR u > n , and solve

33. Example Continued

34. Example: Solve: | 2x -1 | + 4 < 9
1. Isolate the absolute value on the left side to write the inequality in one of the forms:
| u | < n or | u | > n
2a. If | u | < n, then write:
-n < u < n , and solve
2b. If | u | > n, then write:
u < -n or u > n , and solve

35. Example Continued

36. Absolute Value Inequality with No Solution
How can you tell immediately that the following inequality has no solution?
It says that absolute value (or distance) is negative – contrary to the definition of absolute value
Absolute value inequalities of this form always have no solution:

37. Does this have a solution?
At first glance, this is similar to the last example, because “ < 0 “ means negative, and:
However, notice the symbol is:
And it is possible that:
We have previously learned to solve this as:

38. Solve this:
Remember that absolute value of a number is always greater than or equal to zero, therefore the solution will be:
every real number except the one that makes this absolute value equal to zero (the inequality symbol says it must be greater than zero)
Another way of saying this is that: The only bad value of “x” is:
The solution, in interval notation is:

39. Homework Problems Section: 9.2 Page: 635
Problems: Odd: 1, 5 – 31, 35 – 95
MyMathLab Homework Assignment 9.2 for practice
MyMathLab Quiz 9.2 for grade