Lesson 7

Circles in Triangles

Lesson Narrative

In this lesson, students apply what they’ve learned about angle bisectors to construct a triangle’s inscribed circle. Then, students use their knowledge of circumcenters and incenters to prove a property of equilateral triangles.

Students use appropriate tools like tracing paper, straightedge, compass, or dynamic geometry software strategically (MP5) when they construct the inscribed circle of an arbitrary triangle. They have an opportunity to construct a viable argument (MP3) when they write a proof that for an equilateral triangle, the incenter and circumcenter coincide.

Technology isn’t required for this lesson, but there are opportunities for students to choose to use appropriate technology to solve problems. We recommend making technology available.

Learning Goals

Teacher Facing

  • Construct the inscribed circle of a triangle.

Student Facing

  • Let’s construct the largest possible circle inside of a triangle.

Required Materials

Learning Targets

Student Facing

  • I can construct the inscribed circle of a triangle.

CCSS Standards

Building On


Building Towards

Print Formatted Materials

Teachers with a valid work email address can click here to register or sign in for free access to Cool Down, Teacher Guide, and PowerPoint materials.

Student Task Statements pdf docx
Cumulative Practice Problem Set pdf docx
Cool Down Log In
Teacher Guide Log In
Teacher Presentation Materials pdf docx

Additional Resources

Google Slides Log In
PowerPoint Slides Log In