Combine properties of inequality to isolate variables, solve algebraic inequalities, and express their solutions graphically
Simplify and solve algebraic inequalities using the distributive property to clear parentheses and fractions
Combine properties of inequality to solve algebraic inequalities
A popular strategy for solving equations, isolating the variable, also applies to solving inequalities. By adding, subtracting, multiplying and/or dividing, you can rewrite the inequality so that the variable is on one side and everything else is on the other. As with one-step inequalities, the solutions to multi-step inequalities can be graphed on a number line.
Example
Solve for p. 4p+5<29
Show Solution
Begin to isolate the variable by subtracting 5 from both sides of the inequality.
4p+5<29−5−5––––––––––––––4p<24
Divide both sides of the inequality by 4 to express the variable with a coefficient of 1.
4p–––<24–––4<4p<6
Answer
Inequality: p<6
Interval: (−∞,6)
Graph: Note the open circle at the end point 6 to show that solutions to the inequality do not include 6. The values where p is less than 6 are found all along the number line to the left of 6.
Check the solution.
Show Solution
Check the end point 6 in the related equation.
4p+5=29Does4(6)+5=29?24+5=2929=29Yes!
Try another value to check the inequality. Let’s use p=0.
4p+5<29Is4(0)+5<29?0+5<295<29Yes!
p<6 is the solution to 4p+5<29
Example
Solve for x: 3x–7≥41
Show Solution
Begin to isolate the variable by adding 7 to both sides of the inequality, then divide both sides of the inequality by 3 to express the variable with a coefficient of 1.
3x−7≥41+7+7––––––––––––3x3≥483x≥16
Answer
Inequality: x≥16
Interval: [16,∞)
Graph: To graph this inequality, you draw a closed circle at the end point 16 on the number line to show that solutions include the value 16. The line continues to the right from 16 because all the numbers greater than 16 will also make the inequality 3x–7≥41 true.
Check the solution.
Show Solution
First, check the end point 16 in the related equation.
3x−7=41Does3(16)−7=41?48−7=4141=41Yes!
Then, try another value to check the inequality. Let’s use x=20.
3x−7≥41Is3(20)−7≥41?60−7≥4153≥41Yes!
When solving multi-step equations, pay attention to situations in which you multiply or divide by a negative number. In these cases, you must reverse the inequality sign.
Example
Solve for p. −58>14−6p
Show Solution
Note how the variable is on the right hand side of the inequality, the method for solving does not change in this case.
Begin to isolate the variable by subtracting 14 from both sides of the inequality.
−58>14−6p−14−14––––––––––––––––––−72>−6p
Divide both sides of the inequality by −6 to express the variable with a coefficient of 1. Dividing by a negative number results in reversing the inequality sign.
−72–––––>−6p–––––−6−612<p
We can also write this as p>12. Notice how the inequality sign is still opening up toward the variable p.
Answer
Inequality: p>12
Interval: (12,∞)
Graph: The graph of the inequality p > 12 has an open circle at 12 with an arrow stretching to the right.
Check the solution.
Show Solution
First, check the end point 12 in the related equation.
−58=14−6p−58=14−6(12)−58=14−72−58=−58
Then, try another value to check the inequality. Try 100.
−58>14−6p−58>14−6(100)−58>14−600−58>−586
In the following video, you will see an example of solving a linear inequality with the variable on the left side of the inequality, and an example of switching the direction of the inequality after dividing by a negative number.
In the following video, you will see an example of solving a linear inequality with the variable on the right side of the inequality, and an example of switching the direction of the inequality after dividing by a negative number.
Simplify and solve algebraic inequalities using the distributive property
As with equations, the distributive property can be applied to simplify expressions that are part of an inequality. Once the parentheses have been cleared, solving the inequality will be straightforward.
Example
Solve for x. 2(3x–5)≤4x+6
Show Solution
Distribute to clear the parentheses.
2(3x−5)≤4x+66x−10≤4x+6
Subtract 4x from both sides to get the variable term on one side only.
6x−10≤4x+6−4x−4x––––––––––––––––2x−10≤6
Add 10 to both sides to isolate the variable.
2x−10≤6+10+10–––––––––––––––––2x≤16
Divide both sides by 2 to express the variable with a coefficient of 1.
2x–––≤16–––22x≤8
Answer
Inequality: x≤8
Interval: (−∞,8]
Graph: The graph of this solution set includes 8 and everything left of 8 on the number line.
Check the solution.
Show Solution
First, check the end point 8 in the related equation.
Then, choose another solution and evaluate the inequality for that value to make sure it is a true statement. Try 0.
2(3⋅0−5)≤4⋅0+6?2(−5)≤6−10≤6
x≤8 is the solution to (−∞,8]
In the following video, you are given an example of how to solve a multi-step inequality that requires using the distributive property.
Think About It
In the next example, you are given an inequality with a term that looks complicated. If you pause and think about how to use the order of operations to solve the inequality, it will hopefully seem like a straightforward problem. Use the textbox to write down what you think is the best first step to take.
Solve for a. 2a−46<2
Show Solution
Clear the fraction by multiplying both sides of the equation by 6.
2a−46<26⋅2a−46<2⋅62a−4<12
Add 4 to both sides to isolate the variable.
2a−4<12+4+4–––––––––––2a<16
Divide both sides by 2 to express the variable with a coefficient of 1.
2a2<162a<8
Answer
Inequality: a<8
Interval: (−∞,8)
Graph: The graph of this solution contains a solid dot at 8 to show that 8 is included in the solution set. The line continues to the left to show that values less than 8 are also included in the solution set.
Check the solution.
Show Solution
First, check the end point 8 in the related equation.
2a−46=2Does2(8)−46=2?16−46=2126=22=2Yes!
Then choose another solution and evaluate the inequality for that value to make sure it is a true statement. Try 5.
Is2(5)−46<2?10−46<266<21<2Yes!
Summary
Inequalities can have a range of answers. The solutions are often graphed on a number line in order to visualize all of the solutions. Multi-step inequalities are solved using the same processes that work for solving equations with one exception. When you multiply or divide both sides of an inequality by a negative number, you must reverse the inequality symbol. The inequality symbols stay the same whenever you add or subtract either positive or negative numbers to both sides of the inequality.
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Ex: Solve a Two Step Linear Inequality (Variable Left). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/RB9wvIogoEM. License: CC BY: Attribution
Unit 10: Solving Equations and Inequalities, from Developmental Math: An Open Program. Provided by: Monterey Institute of Technology and Education. Located at: http://nrocnetwork.org/dm-opentext. License: CC BY: Attribution
Ex: Solve a Two Step Linear Inequality (Variable Right). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/9D2g_FaNBkY. License: CC BY: Attribution
Ex: Solve a Linear Inequality Requiring Multiple Steps (One Var). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/vjZ3rQFVkh8. License: CC BY: Attribution
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CC licensed content, Original
Revision and Adaptation. Provided by: Lumen Learning. License: CC BY: Attribution
CC licensed content, Shared previously
Ex: Solve a Two Step Linear Inequality (Variable Left). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/RB9wvIogoEM. License: CC BY: Attribution
Unit 10: Solving Equations and Inequalities, from Developmental Math: An Open Program. Provided by: Monterey Institute of Technology and Education. Located at: http://nrocnetwork.org/dm-opentext. License: CC BY: Attribution
Ex: Solve a Two Step Linear Inequality (Variable Right). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/9D2g_FaNBkY. License: CC BY: Attribution
Ex: Solve a Linear Inequality Requiring Multiple Steps (One Var). Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. Located at: https://youtu.be/vjZ3rQFVkh8. License: CC BY: Attribution