Reflection: Shared Expectations Definition of Similarity and Similar Triangles  Section 2: Practice: Similar Polygons
Since my students have solved problems using proportional reasoning prior to entering this class, I didn’t want to reteach skills I knew they would be able to bring back on their own. Instead, I wanted to focus students’ attention on why and how they could solve similar polygons.
As students worked through this set of practice problems, I asked them to consider a pair of questions that would encourage metacognition, which I posted on the board using the document camera. I posed two questions to them: why can I do this? (when they used a particular solving strategy) and how do I know I can compare these sides? (when they looked for pairs of corresponding sides).
By giving students a frame for working through these problems, I hoped to encourage them to solve in multiple ways that would make sense to them so long as they could justify which sides were corresponding and why their problem solving method made sense. As I circulated the room while students corrected their work, I could see them connecting their work to the approaches shown in the answer key, which allowed me to see how they made sense of solving polygons in multiple ways.
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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 LESSON 2: Similarity Problem Solving and Proofs
 LESSON 3: Similarity Group Assessment
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