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Definition of Similarity and Similar Triangles
Lesson 1 of 11
Objective: SWBAT apply the definition of similarity to identify measurements in similar figures. SWBAT to argue that HL is a “similarity shortcut” for right triangles.
Launch Similarity
 Starting with the Facilitator, students will share out counterclockwise
 The Recorder/Reporter will document:
 The shape that is the exception in each set
 What they noticed about the corresponding sides and angles for each figure in the set
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Practice: Similar Polygons
A number of big ideas were introduced during the Launch section of this lesson. To give my students some time to think about what we've covered so far I will give them some familiar problems to work on. I plan to have students, in pairs, practice applying the definition of similarity to solve for missing angles and side lengths. After about 10 minutes of work time, I will pass out answer keys so that students can make corrections and ask clarifying questions.
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Something I Heard that Reinforced My Current Understanding of Similarity 
Something I Heard that Challenged My Understanding of Similarity 


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Check for Understanding
Because we've done a lot of partner work during this initial similarity lesson, I want to provide my students with an opportunity to share their own thinking. On the back of the Graphic Organizer students used during the wholeclass discussion, I have provided a quick assessment. The assessment checks students' understanding (see page 2) by asking them to determine whether the triangles are similar. I make clear to students that I want them to take their time and use precise academic and geometric vocabulary to explain what they know and how they know it (MP6). In order to get a sense of the connectedness or depth of a student's understanding, I ask the students to show how they know in more than one way. Asking students to provide multiple explanations will give me greater insight into their thinking and understanding.
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I want students to apply what they learned in this lesson, which is why I give them this homework assignment. In Are the Triangles Similar?, students determine whether given pairs triangles are similar and justify how they know by showing work and writing similarity statements.
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