Lesson 8

Reasoning About Equations

These materials, when encountered before Algebra 1, Unit 2, Lesson 8 support success in that lesson.

Lesson Narrative

The mathematical purpose of this lesson is to help students connect back to their knowledge of maintaining equivalent equations by using acceptable moves. Students continue to use hanger diagrams to help them recall justifications for moves that preserve equivalence.

During the practice section of the lesson, students work with geometric formulas, solving repeatedly for the same unknown value with the explicit encouragement to express regularity in repeated reasoning (MP8).

This lesson prepares students to begin the work in the associated Algebra 1 lesson by continuing to emphasize acceptable moves when manipulating equations and previewing the concept of isolating a variable of interest in a formula with multiple variables. It’s not important in this lesson to explicitly connect the two concepts. That will take place in the associated Algebra 1 lesson.

Learning Goals

Teacher Facing

  • Understand solving equations as a process of reasoning and explain the reasoning.

Student Facing

  • Let’s justify the steps of solving an equation.

CCSS Standards


Building Towards