Lesson plan

Understand the triangle inequality theorem by discovering the relationship between angles and their opposite segments in a triangle

teaches Common Core State Standards CCSS.Math.Content.HSG-CO.C.10 http://corestandards.org/Math/Content/HSG/CO/C/10
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3
teaches Common Core State Standards CCSS.Math.Practice.MP5 http://corestandards.org/Math/Practice/MP5
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Big Ideas: Students will be able to decide if three lengths can make a triangle. Students will be able to find the range of possible lengths of the third side when given two sides. Students will be able to use the angle and side inequalities of a triangle to determine the biggest and smallest angles and sides of a triangle. This lesson plan highlights the inequalities in one triangle. By the end of the lesson, students should be able to conceptually understand why the inequalities work and apply them to solve problems. This lesson is taught after students have learned basic constructions, but before students have learned other theorems about triangles. This lesson is the first lesson students learn about triangles. Vocabulary: inequality, sum Special Materials: Popsicle sticks or straws for building triangles. Geogebra or other geometric software (optional)