Undefined Terms of Geometry Lesson Plan

Instructor: Tammy Galloway

Tammy teaches business courses at the post-secondary and secondary level and has a master's of business administration in finance.

Most students believe geometry is a challenging subject; however, they will have fun learning about undefined terms in this lesson. Students will watch a video, answer discussion questions, complete an activity, and take a quiz.

Learning Objectives

After this lesson, students will be able to:

  • define and list the characteristics of a point
  • describe a line and explain how it is geometrically written
  • discuss the geometric shape of a plane
  • describe a set and write an example


60 minutes; extension (optional) 30 minutes

Curriculum Standards

  • CCSS.Math.Content.HSG.CO.A.1

Know precise definitions of angle, circle, perpendicular line, parallel line, and line segment, based on the undefined notions of point, line, distance along a line, and distance around a circular arc.

  • CCSS.Math.Content.HSG.CO.A.2

Represent transformations in the plane using, e.g., transparencies and geometry software; describe transformations as functions that take points in the plane as inputs and give other points as outputs. Compare transformations that preserve distance and angle to those that do not (e.g., translation versus horizontal stretch).



  • Begin the lesson by asking students to discuss one concept they know about geometry.
  • Then explain that this lesson explores four undefined geometry terms.
  • Distribute the Undefined Terms of Geometry: Concepts & Significance lesson, play the video, pause at 1:50, then start the following discussion:
    • What are undefined terms of geometry?
    • Define a point and discuss their purpose.
  • Now restart the video, pause at 3:57, then pose the following:
    • How does the author define a line?
    • How are lines labeled?
    • What are planes?
  • Next play the video until the end, then ask students to explain a set and how they are written.
  • Afterwards, show the lesson quiz, pair students and ask them to answer each question.
  • Then review for accuracy.

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