Lesson plan

Identify measurements for missing interior and exterior angles using informal arguments

teaches Common Core State Standards CCSS.Math.Content.8.G.A.5 http://corestandards.org/Math/Content/8/G/A/5

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Big Ideas: An exterior angle of a triangle is equal to the sum of the remote interior angles in relation to that exterior angle. Equivalence of angles can be represented in many ways. Students will look at multiple paths for finding the same angle measures. They will compare paths for finding exterior angles either by using the relationship between exterior and remote interior angles or by looking at the relationships formed with supplementary lines and the triangle angle sum. Students will use mathematical reasoning to justify their solutions. Students will draw on the relationship of supplementary angles learned in grade 7 as well as the triangle angle sum relationship from previous lessons in grade 8. Vocabulary: exterior angle of a triangle, remote interior angles of a triangle, supplementary, triangle angle sum