Lesson plan

Understand the triangle midsegment theorem by using constructions

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.MP1 http://corestandards.org/Math/Practice/MP1
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: A midsegment connecting two sides of a triangle is parallel to the third side and half its length. This lesson takes place after the students have learned how to construct perpendicular bisectors and have proven the triangle angle sum theorem. This lesson could take place before or after the lessons on the centers of a triangle, but it is suggested that it is taught after since students will have more practice constructing midpoints. That knowledge will help make the launch activity go smoother. Students should prove the triangle midsegment theorem when they learn about triangle similarity. Vocabulary: midpoint, midsegment, parallel Special Materials: Pencil Paper Straightedge Compass