Mathematics
Grade 8
15 min
Graph solutions to multi-step inequalities
Graph solutions to multi-step inequalities
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1
Introduction & Learning Objectives
Learning Objectives
Solve multi-step inequalities using inverse operations.
Correctly apply the rule for reversing the inequality sign when multiplying or dividing by a negative number.
Represent the solution set of an inequality on a number line using appropriate open or closed circles.
Accurately shade the correct direction on a number line to represent the solution set.
Identify and correct common errors made when solving and graphing multi-step inequalities.
Interpret the meaning of an inequality's solution set in context.
Ever wonder how stores decide what price to put on a sale item, or how much you can spend without going over budget? 💰 Inequalities help us answer these 'at most' or 'at least' questions!
In this lesson, you'll learn how...
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Key Concepts & Vocabulary
TermDefinitionExample
InequalityA mathematical statement that compares two expressions using an inequality symbol (<, >, ≤, ≥, ≠).2x + 3 > 7
Multi-step InequalityAn inequality that requires two or more inverse operations to isolate the variable.5x - 8 ≤ 12 or 3(x + 1) > 9
Solution SetThe set of all numbers that make an inequality true. Unlike equations, inequalities often have infinitely many solutions.For x > 3, the solution set includes all numbers greater than 3 (e.g., 3.1, 4, 100).
Number LineA visual representation of numbers in order, used to graph the solution set of an inequality.A line with evenly spaced tick marks representing integers, with arrows on both ends.
Open CircleA hollow circle on a number line used to indicate that the endpoint is NOT included in the s...
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Core Formulas
Inverse Operations for Inequalities
To solve an inequality, apply inverse operations to both sides to isolate the variable, just like with equations.
If $a < b$, then:
$a + c < b + c$
$a - c < b - c$
Addition and subtraction maintain the direction of the inequality. Use these to move constant terms or variable terms to one side.
Multiplication/Division by a Positive Number
If $a < b$, and $c > 0$ (c is positive), then:
$a \cdot c < b \cdot c$
$\frac{a}{c} < \frac{b}{c}$
Multiplying or dividing both sides of an inequality by a positive number does NOT change the direction of the inequality sign.
Multiplication/Division by a Negative Number
If $a < b$, and $c < 0$ (c is negative), then:
$a \cdot c > b \cdot c$
$\frac{a}{c} > \frac{b}{c}...
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Challenging
Which graph represents the solution to the inequality (1/2)x - 3 ≥ (1/4)x - 1?
A.An open circle on 8, shaded to the right.
B.closed circle on 8, shaded to the right.
C.closed circle on 8, shaded to the left.
D.closed circle on 4, shaded to the right.
Challenging
You are saving for a new bike that costs at least $375. You have already saved $65. You earn $10 per hour for babysitting. Which graph shows the number of hours, h, you need to work to afford the bike?
A.closed circle on 31, shaded to the right.
B.An open circle on 31, shaded to the right.
C.closed circle on 31, shaded to the left.
D.closed circle on 44, shaded to the right.
Challenging
For which of the following inequalities is x = -2 a possible solution?
A.4(x - 1) > 2x - 6
B.8 - x ≤ 3x + 15
C.5x + 9 > -1
D.2(3x + 7) ≤ -x
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