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Lesson plan

Lesson 26: Testing Points to Solve Inequalities

teaches Common Core State Standards MP7 http://corestandards.org/Math/Practice/MP7
teaches Common Core State Standards MP3 http://corestandards.org/Math/Practice/MP3
teaches Common Core State Standards 8.EE.C.7.b http://corestandards.org/Math/Content/8/EE/C/7/b
teaches Common Core State Standards 8.EE.C.7 http://corestandards.org/Math/Content/8/EE/C/7

Lesson 26: Testing Points to Solve Inequalities

The mathematical purpose of this lesson is to give students a chance to name and analyze common incomplete strategies and concepts when working with inequalities. Students engage in error analysis on the topic of testing points around a given boundary to determine which half of the real number line contains solutions to an inequality, and on the the topic of solving equations.

Error analysis around solving equations helps students continue to hone the foundational skill of solving equations, which is useful for finding the boundary point of the solutions of a linear inequality. Exploring the reasoning behind testing points helps students make strategic choices as they solve inequalities.

In the supported Algebra 1 lesson, students are using their understanding of systems of inequalities with two variables to create a mathematical model for designing trail mix.

Students have the opportunity to construct viable arguments and critique the reasoning of others (MP3) as they engage in error analysis.

Lesson overview

  • 26.1 Warm-up: Math Talk: Solving Equations (10 minutes)
  • 26.2 Activity: Character Chat (20 minutes)
  • 26.3 Activity: Error! (15 minutes)

Learning goals:

  • Analyze common errors when solving linear equations.
  • Understand the purpose, when solving inequalities, of testing points on either side of the solution to the related equation.

Learning goals (student facing):

  • Let’s critique some peoples’ reasoning.


  • This lesson builds towards the standards: CCSS.HSA-REI.B.3MS.A-REI.3MO.A1.CED.A.1






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