Lesson plan

7. Apply triangle angle sum to polygons (A)

teaches Common Core State Standards CCSS.Math.Content.8.G.A.5 http://corestandards.org/Math/Content/8/G/A/5
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3
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Lesson objective: Apply the triangle angle sum to polygons.

This lesson provides an opportunity for students to apply their knowledge and understanding of triangle angle sum to a mathematical situation. Students are asked to determine the interior angle sums of different polygons, analyze their results, and create a rule that determines the interior angle sum of any polygon. 

Key Concept students will use: 

  • The angle sum for any triangle is 180 degrees, and we can informally prove this using the relationships of angles.

Skills students will use:

  • angle sum of a triangle

Students engage in Mathematical Practice #3 (construct viable arguments and critique the reasoning of others) as they make conjectures about the polygon angle sum, justify their conclusions, and communicate them to others.

Key vocabulary: 

  • polygon
  • triangle angle sum

Special materials needed:

  • polygon templates (optional)