Mathematics
Grade 9
15 min
Graph a two-variable linear inequality
Graph a two-variable linear inequality
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1
Introduction & Learning Objectives
Learning Objectives
Identify the boundary line for a given two-variable linear inequality.
Determine whether the boundary line should be solid or dashed based on the inequality symbol.
Graph the boundary line on a coordinate plane accurately.
Select an appropriate test point and use it to determine which half-plane to shade.
Correctly shade the solution region on the coordinate plane.
Interpret the graph as the set of all solutions to the inequality.
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This tutorial will guide you through the process of graphing two-variable linear inequalities. You'll learn how to turn an inequality into a vi...
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Key Concepts & Vocabulary
TermDefinitionExample
Linear Inequality in Two VariablesA mathematical statement that compares two expressions using an inequality symbol (<, >, ≤, ≥), where at least one expression contains two variables (like x and y) raised to the power of 1.y < 2x + 5 or 4x - 3y ≥ 12
Boundary LineThe line that separates the coordinate plane into two regions, or half-planes. It represents the 'equals' part of the inequality.For the inequality y > x - 3, the boundary line is the equation y = x - 3.
Half-PlaneOne of the two regions of the coordinate plane created by the boundary line. All the points in one half-plane are solutions to the inequality, while the points in the other are not.The graph of y > x - 3 has a boundary line y = x - 3, which divides the plane into an upper ha...
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Core Formulas
Boundary Line Type
For inequalities with > or <, use a DASHED line. For inequalities with ≥ or ≤, use a SOLID line.
A dashed line shows that the points on the line are NOT part of the solution. A solid line shows that the points on the line ARE part of the solution.
Test Point Method for Shading
1. Choose a point not on the line (e.g., (0,0)). 2. Substitute its coordinates into the original inequality. 3. If the result is TRUE, shade the half-plane containing the test point. 4. If the result is FALSE, shade the other half-plane.
This is the most reliable method to determine which region represents the solution set. Always use the original inequality for the test to avoid errors from rearranging the equation.
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Challenging
The graph of a linear inequality is a solid line passing through (-3, 0) and (0, 2). The point (1, 1) is NOT in the shaded solution region. Which inequality is represented by the graph?
A.y ≤ (2/3)x + 2
B.y ≥ (2/3)x + 2
C.y ≥ (3/2)x + 2
D.y ≤ (-2/3)x - 2
Challenging
To graph the inequality 2x - 5y ≤ 0, you find the boundary line y = (2/5)x passes through the origin. You choose (5, 1) as a test point. What should you conclude?
A.The test is true (10 ≤ 5), so shade the half-plane containing (5, 1).
B.The test is false (5 ≤ 10), so shade the half-plane containing (5, 1).
C.The test is false (5 ≤ 10), so shade the half-plane NOT containing (5, 1).
D.The test is true (10 ≤ 5), so shade the half-plane NOT containing (5, 1).
Challenging
The inequality Ax - 3y ≤ 12 has a boundary line that passes through the point (3, -2). The graph is shaded above the line. What is the value of A?
A.= 2
B.= 6
C.= -2
D.= 4
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