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Lesson Plan

Prove and apply the conjecture that a line dividing two sides of a triangle proportionally is parallel to the third side by using the properties of similarity

teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Content.HSG-SRT.B.4 http://corestandards.org/Math/Content/HSG/SRT/B/4
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3
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Big Ideas: We can use similarity to prove theorems about triangles.If segments of two sides of a triangle are divided by a line that creates proportional segments, that line is parallel to the third side of the triangle. The tasks in this lesson require students to show that a line is parallel to the third side of a triangle if it creates segments of the other two sides that are proportional. Students will use prior knowledge of parallel lines, similarity, and the AA similarity criteria to prove the proportion. This lesson leads into solving problems involving similar triangles and right triangle trigonometry. Vocabulary: Similarity Proportionality
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