Lesson plan

Lesson 14: Coordinate Proof

teaches Common Core State Standards MP5 http://corestandards.org/Math/Practice/MP5
teaches Common Core State Standards MP6 http://corestandards.org/Math/Practice/MP6
teaches Common Core State Standards MP3 http://corestandards.org/Math/Practice/MP3
teaches Common Core State Standards HSG-GPE.B.7 http://corestandards.org/Math/Content/HSG/GPE/B/7
teaches Common Core State Standards HSG-GPE.B.5 http://corestandards.org/Math/Content/HSG/GPE/B/5
teaches Common Core State Standards HSG-GPE.B.4 http://corestandards.org/Math/Content/HSG/GPE/B/4
teaches Common Core State Standards HSG-C.A.2 http://corestandards.org/Math/Content/HSG/C/A/2

Lesson 14: Coordinate Proof

In this lesson, students use coordinates to make conjectures and prove simple geometric theorems algebraically. They begin with some informal reasoning in a “Which One Doesn’t Belong” prompt. In the next activity, students use slopes to classify a quadrilateral. Then, they use inductive reasoning to observe a pattern and make a conjecture which will be generalized in a subsequent unit. Students have an opportunity to attend to precision in mathematical language (MP6) as they write and refine their conjectures. At the end of the lesson, students critique each other’s reasoning (MP3) about properties of the quadrilaterals from the warm-up.

One of the activities in this lesson works best when each student has access to devices that can run the Desmos applet, because students will benefit from seeing the relationship in a dynamic way.

Lesson overview

  • 14.1 Warm-up: Which One Doesn’t Belong: Coordinate Quadrilaterals (5 minutes)
  • 14.2 Activity: Name This Quadrilateral (15 minutes)
    • Includes "Are you Ready for More?" extension problem 
  • 14.3 Activity: Circular Logic (15 minutes)
  • Lesson Synthesis
  • 14.4 Cool-down: Name That Quadrilateral (5 minutes) 

Learning goals:

  • Prove simple geometric theorems algebraically using coordinates.

Learning goals (student facing):

  • Let’s use coordinates to prove theorems and to compute perimeter and area.

Learning targets (student facing):

  • I can use coordinates of figures to prove geometric theorems.

Required materials:

  • Geometry toolkits 
  • Graph paper

Required preparation:

  • Devices and index cards are required for the digital version of the Circular Logic task. 


  • This lesson builds towards the standard: CCSS.HSG-GPE.B.4MS.G-GPE.4MO.G.GPE.B.3






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