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2.8 Solving Linear Inequalities

# 2.8 Solving Linear Inequalities

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2.8 Solving Linear Inequalities. Definition. An inequality is an algebraic expression related by < “is less than,” ≤ “is less than or equal to,” > “is greater than,” or ≥ “is greater than or equal to.”. Linear Inequality in One Variable - PowerPoint PPT Presentation

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2.8 Solving Linear Inequalities

2.8 Solving Linear InequalitiesDefinition.An inequality is an algebraic expression related by< is less than, is less than or equal to,> is greater than, or is greater than or equal to.We solve an inequality by finding all real number solutions of it. For example, the solution set {x | x 2} includes all real numbers that are less than or equal to 2, not just the integers less than or equal to 2.Slide 2.8-3Linear Inequality in One VariableA linear inequality in one variable can be written in the form

where A, B, and C represent real numbers, and A 0.

Objective 1 Graph intervals on a number line.Slide 2.8-4Graphing is a good way to show the solution set of an inequality. We graph all the real numbers belonging to the set {x | x 2} by placing a square bracket at 2 on a number line and drawing an arrow extending from the bracket to the left (to represent the fact that all numbers less than 2 are also part of the graph).

Slide 2.8-5Graph intervals on a number line. The set of numbers less than or equal to 2 is an example of an interval on the number line. To write intervals, we use interval notation. For example, the interval of all numbers less than or equal to 2 is written (, 2]. The negative infinity symbol does not indicate a number, but shows that the interval includes all real numbers less than 2.As on the number line, the square bracket indicates that 2 is part of the solution.A parentheses is always used next to the infinity symbol. The set of real numbers is written as (, ).Slide 2.8-6Graph intervals on a number line. (contd)Write each inequality in interval notation, and graph the interval.Solution: Solution:

Slide 2.8-7Graphing Intervals on a Number Line

CLASSROOM EXAMPLE 1Keep the following important concepts regarding interval notation in mind: 1. A parenthesis indicates that an endpoint is not included in a solution set.Slide 2.8-8Graph intervals on a number line. (contd)Some texts use a solid circle rather than a square bracket to indicate the endpoint is included in a number line graph. An open circle is used to indicate noninclusion, rather than a parentheses.2. A bracket indicates that an endpoint is included in a solution set.3. A parenthesis is always used next to an infinity symbol, or .4. The set of all real numbers is written in interval notation as (,).Objective 2 Use the addition property of inequality.Slide 2.8-9Slide 2.8-10Addition Property of InequalityIf A, B, and C represent real numbers, then the inequalities

and

Have exactly the same solutions.That is, the same number may be added to each side of an inequality without changing the solutions.

Use the addition property of inequality.

As with the addition property of equality, the same number may be subtracted from each side of an inequality.Slide 2.8-11Use the addition property of inequality. (contd) Because an inequality has many solutions, we cannot check all of them by substitutions as we did with the single solution of an equation. Thus, to check the solutions of an inequality, first substitute into the equation the boundary point of the interval and another number from within the interval to test that they both result in true statements. Next, substitute any number outside the interval to be sure it gives a false statement.

CLASSROOM EXAMPLE 2Solve the inequality, and graph the solution set.Solution:

Slide 2.8-12Using the Addition Property of InequalityObjective 3 Use the multiplication property of inequality.Slide 2.8-13Now multiply by each side of 3 < 7 by the negative number 5.Multiply each side of the inequality 3 < 7 by the positive number 2.To get a true statement when multiplying each side by 5, we must reverse the direction of the inequality symbol.The addition property of inequality cannot be used to solve an inequality such as 4x 28. This inequality requires the multiplication.

True

False

TrueSlide 2.8-14Use the multiplication property of inequality. As with the multiplication property of inequality, the same nonzero number may be divided into each side of an inequality.Multiplication Property of InequalityIf A, B, and C, with C 0,1. if C is positive, then the inequalitiesand have exactly the same solutions;2. if C is negative, then the inequalities and have exactly the same solutions.That is, each of an inequality may be multiplied by the same positive number without changing the solutions. If the multiplier is negative, we must reverse the direction of the inequality symbol.

Slide 2.8-15Use the multiplication property of inequality. (contd)

Solution:

Solve the inequality, and graph the solution set.Slide 2.8-16Using the Multiplication Property of InequalityCLASSROOM EXAMPLE 3Objective 4 Solve linear inequalities by using both properties of inequality.Slide 2.8-17Solving a Linear InequalityStep 1: Simplify each side separately. Use the distributive property to clear parentheses and combine like terms on each side as needed.Step 2: Isolate the variable terms on one side. Use the addition property of inequality to get all terms with variables on one side of the inequality and all numbers on the other side.Step 3: Isolate the variable. Use the multiplication property of inequality to change the inequality to the form variable < k or variable > k, where k is a number.Remember: Reverse the direction of the inequality symbol only when multiplying or dividing each side of an inequality by a negative number..Slide 2.8-18Solve linear inequalities by using both properties of inequality.

Solution:

Solve the inequality, and then graph the solution set.Slide 2.8-19Solving a Linear InequalityCLASSROOM EXAMPLE 4

Solution:

Solve the inequality, and graph the solution set.Slide 2.8-20Solving a Linear InequalityCLASSROOM EXAMPLE 5Solve and graph the solution set.

Multiply by 4.Distributive property.Multiply.Subtract 11.Distributive property.Slide 2.8- 20CLASSROOM EXAMPLE 6Solving a Linear Inequality with FractionsSolution:

Reverse the inequality symbol when dividing by a negative number.

[Subtract 11.Subtract 3m.Divide 2.Slide 2.8- 21Solving a Linear Inequality with Fractions (contd)The solution set is the interval [13/2, ).CLASSROOM EXAMPLE 6Objective 5 Solve applied problems by using inequalities.Slide 2.8-23Inequalities can be used to solve applied problems involving phrases that suggest inequality. The table gives some of the more common such phrases, along with examples and translations.

In general, to find the average of n numbers, add the numbers and divide by n. We use the same six problem-solving steps from Section 2.4, changing Step 3 to Write an inequality., instead of Write an equation.

Do not confuse statements such as 5 is more than a number with phrases like 5 more than a number. The first of these is expressed as 5 > x, while the second is expressed as x + 5 or 5 + x.Slide 2.8-24Solve applied problems by using inequalities. A rental company charges \$5 to rent a leaf blower, plus \$1.75 per hr. Marge Ruhberg can spend no more than \$26 to blow leaves from her driveway and pool deck. What is the maximum amount of time she can use the rented leaf blower?

Step 1Read the problem again. What is to be found?The maximum time Marge can afford to rent the blower.What is given?The flat rate to rent the leaf blower, the additional hourly charge to rent the leaf blower, and the maximum amount that Marge can spend.

Step 2Assign a variable. Let h = the number of hours she can rent the blower.Slide 2.5- 24CLASSROOM EXAMPLE 7Using a Linear Inequality to Solve a Rental ProblemSolution:Step 3Write an inequality. She must pay \$5, plus \$1.75 per hour for h hours and no more than \$26.Cost of is no renting more than 26 5 + 1.75h 26

Step 4Solve. 1.75h 21 h 12Step 5State the answer.She can use the leaf blower from a maximum of 12 hours.Step 6Check.If she uses the leaf blower for 12 hr, she will spend5 + 1.75(12) = 26 dollars, the maximum.Slide 2.5- 25CLASSROOM EXAMPLE 7Using a Linear Inequality to Solve a Rental Problem (contd)Subtract 5.Divide by 1.75.Solution: Let x = Maggies fourth test score.

Maggie must get greater than or equal to an 88. Maggie has scores of 98, 86, and 88 on her first three tests in algebra. If she wants an average of at least 90 after her fourth test, what score must she make on that test?Slide 2.8-27Finding an Average Test ScoreCLASSROOM EXAMPLE 8Objective 6 Solve linear inequalities with three parts.Slide 2.8-28Inequalities that say the one number is between two other numbers are three-part inequalities. For example, says that 5 is between 3 and 7.

For some applications, it is necessary to work with a three-part inequality such as where x +2 is between 3 and 8. To solve this inequality, we subtract 2 from each of the three parts of the inequality.

Slide 2.8-29Solve linear inequalities with three parts. The idea is to get the inequality in the forma number < x < another number,using is less than. The solution set can then easily be graphed.

When inequalities have three parts, the order of the parts is important. It would be wrong to write an inequality as 8 < x + 2 < 3, since this would imply 8 < 3, a false statement. In general, three-part inequalities are written so that the symbols point in the same direction and both point toward the lesser number.Slide 2.8-30Solve linear inequalities with three parts. (contd) Write the inequality in interval notation, and graph the interval.Solution:

Slide 2.8-31Solving Three-Part Inequalities

CLASSROOM EXAMPLE 9Solve the inequality, and graph the solution set.

Solution:

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