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F – Inequalities, Lesson 4, Graphing Linear Inequalities (r. 2018)
INEQUALITIES
Graphing Linear Inequalities
Common Core Standard A-REI.12 Graph the solutions to a linear inequality in two variables as a half-plane (excluding the boundary in the case of a strict inequality), and graph the solution set to a system of linear inequali- ties in two variables as the intersection of the corre- sponding half-planes.
Next Generation Standard AI-A.REI.12 Graph the solutions to a linear inequality in two variables as a half-plane (excluding the boundary in the case of a strict inequality), and graph the solution set to a system of linear inequalities in two variables as the intersection of the corresponding half-planes. Note: Graphing linear equations is a fluency recom- mendation for Algebra I. Students become fluent in solving characteristic problems involving the analytic geometry of lines, such as writing down the equation of a line given a point and a slope. Such fluency can support them in solving less routine mathematical problems involving linearity; as well as modeling lin- ear phenomena (including modeling using systems of linear inequalities in two variables).
LEARNING OBJECTIVES
Students will be able to:
- Graph a single inequality involving two variables on a coordinate plane. a. Determine if the boundary line is a solid line or a dashed line. b. Determine if the solution set is shaded above or below the boundary line.
Overview of Lesson Teacher Centered Introduction Overview of Lesson
**- activate students’ prior knowledge
- vocabulary
- learning objective(s)
- big ideas: direct instruction
- modeling**
Student Centered Activities guided practice Teacher: anticipates, monitors, selects, sequences, and connects student work
**- developing essential skills
- Regents exam questions
- formative assessment assignment (exit slip, explain the math, or journal entry)**
VOCABULARY
boundary line dashed line linear inequality
shading solid line solution set
testing a solution
BIG IDEAS
A linear inequality describes a region of the coordinate plane that has a boundary line. Every point in the region is a solution of the inequality.
The solution set of a linear inequality includes all ordered pairs that make the inequality true. The graph of an inequality represents the solution set.
Graphing a Linear Inequality Step One. Change the inequality sign to an equal sign and graph the boundary line in the same manner that you would graph a linear equation. When the inequality sign contains an equality bar beneath it, use a solid line for the boundary. Any point (ordered pair) on the boundary line is part of the solution set. When the inequality sign does not contain an equality bar beneath it, use a dashed line for the boundary. Any point (ordered pair) on the boundary line is not part of the solution set. Step Two. Restore the inequality sign and test a point to see which side of the boundary line the solution is on. The point (0,0) is a good point to test since it simplifies any multiplication. However, if the boundary line passes through the point (0,0), another point not on the boundary line must be selected for testing. If the test point makes the inequality true, shade the side of the boundary line that includes the test point. If the test point makes the inequality not true, shade the side of the boundary line does not include the test point. NOTE: If the dependent variable is isolated in the left expression of the inequality, a simplified way to determine which side of the line to shade is as follows:
- If the inequality sign contains >, shade above the boundary line. o Examples: y > x and y ≥ x are shaded above the boundary line.
- If the inequality sign contains <, shade below the boundary line. o Examples: y^ <^ x and^ y^ ≤^ x are shaded^ below^ the boundary line.
Example Graph First , change the inequality sign an equal sign and graph the line:. This is the boundary line of the solution. Since there is no equality line beneath the inequality symbol, use a dashed line for the boundary. NOTE: A graphing calculator can be used if the inequality has the dependent variable isolated as the in the left expression of the inequality
Next , test a point to see which side of the boundary line the solution is on.^ Try (0,0), since it makes the multiplication easy, but remember that any point will do.
y < 2 x + 3 y = 2 x + 3
STEP 4. Inspect the graph to determine if the point (3,8) is included in the solution set. It is not. STEP 5. Do a check to see if the point (3,8) makes the original inequality true.
25 14 not true
x + y ≤ y +
Since the inequality is not true for the point (3,8), the point is not in the solution set.
REGENTS EXAM QUESTIONS (through June 2018)
A.REI.D.12: Graphing Linear Inequalities
Which inequality is represented in the graph below?
On the set of axes below, graph the inequality.
Which inequality is represented by the graph below?
Shawn incorrectly graphed the inequality as shown below:
Explain Shawn’s mistake.
Graph the inequality correctly on the set of axis below.
SOLUTIONS
- ANS: 1 Strategy: Use the slope intercept form of a line, , to construct the inequality from the graph.
The line passes though points (0,4) and (1,1), so the slope is. The y-intercept is 4.
The equation of the boundary line is , so eliminate choices c and d. The shading is above the line, so eliminate choice b. The inequality is , so answer choice a is correct.
PTS: 2 NAT: A.REI.D.12 TOP: Linear Inequalities
- ANS:
Strategy: Transpose the inequality, put it in a graphing calculator, then use the table and graph views to create the graph on paper.
STEP 1. Transpose the inequality for input into a graphing calculator.
STEP 2. Inpout the inequality into a graphing calculator.
STEP 3. Use information from the graph and table views to create the graph on paper. Be sure to make the line dotted.
PTS: 2 NAT: A.REI.D.12 TOP: Graphing Linear Inequalities
- ANS: 2 PTS: 2 NAT: A.REI.D.12 TOP: Graphing Linear Inequalities
- ANS:
Shawn’s mistake was he shaded the wrong side of the boundary line.
Shawn’s y-intercept is correct. Shawn’s slope is correct. Shawn correctly graphed a solid boundary line. Shawn’s mistake was he shaded the wrong side of the boundary line.
PTS: 2 NAT: A.REI.D.12 TOP: Graphing Linear Inequalities
