Lesson plan

Prove and apply relationships between the angles of parallelograms by using congruent triangles

teaches Common Core State Standards CCSS.Math.Content.HSG-CO.C.11 http://corestandards.org/Math/Content/HSG/CO/C/11

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Big Ideas: Congruent triangles can be used to prove properties of parallelograms. In this lesson students will formalize their previous observations about the angles of a parallelogram through proof. The lesson focuses on the concept that opposite angles are congruent, but students may also observe that adjacent angles are supplementary. Vocabulary: congruent, opposite angles, adjacent angles, parallelogram, supplementary, opposite sides Special Materials: None.