Lesson 13

Using Equations to Solve for Unknown Angles

Lesson Narrative

In the previous lesson, students saw that equations could be used to represent relationships between angles. In this lesson, students practice writing and solving equations of the form \(px + q = r\) in the context of finding unknown angle measures. This brings together their work with equations from the previous unit and their work with angles from earlier lessons in this unit, giving students a chance to build fluency with both of these concepts.

Teacher Notes for IM 6–8 Math Accelerated
This lesson is optional. Use this lesson if students need additional practice writing and solving equations.

Learning Goals

Teacher Facing

  • Critique whether a given equation represents the relationship between angles in a diagram.
  • Solve an equation that represents a relationship between angle measures, and explain (in writing and using other representations) the reasoning.
  • Write an equation of the form $px+q=r$ or $p(x+q)=r$ to represent the relationship between angles in a given diagram.

Student Facing

Let’s figure out missing angles using equations.

Learning Targets

Student Facing

  • I can write an equation to represent a relationship between angle measures and solve the equation to find unknown angle measures.

CCSS Standards

Building On


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