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# 2 Triangles in 1

Lesson 4 of 8

## Objective: SWBAT prove that a line parallel to one side of a triangle divides the other two proportionally while using AA criterion.

#### Do Now

*10 min*

In this Do Now, students will have an opportunity to review solving proportions. In this lesson, students will be required to set-up and solve proportions to find the lengths of sides (and parts of sides) of triangles.

You can ask students to come to board and share their work (MP 3) on this Do Now as it is a pre-requisite skill.

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#### Avatar Video and Exploration

*30 min*

I would suggest that the last 4 minutes of the video are most useful in starting a conversation with students about similarity. Most of my students had seen Avatar so the introductory material may be unnecessary if you are limited on time.

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In the Activity-Homework for this lesson, students will work on using concepts about similar triangles and proportionality to complete practice questions. The questions for #6-9 are great problems to review with students since #6-8 review using the concepts of proportionality to find length measures in triangles. Question 9 requires students to look for regularity in repeated reasoning. Students must remember that when two consecutive interior angles are supplementary, it means that lines are parallel (MP 8).

The Exit Ticket can used use as a formative assessment to ensure that students understand the key concepts in today's lesson. This is particularly important since the lesson after this, Similiarity Applied, will ask students to persevere through more challenging questions.

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I was looking forward to trying this lesson with my Geometry students next week, but have not had success in finding the video you used as a starting point. Do you have an alternate link? Thanks for your help!

https://www.youtube.com/watch?v=KezEULMEvhq

| 10 months ago | Reply

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- UNIT 1: Introduction to Geometry: Points, Lines, Planes, and Angles
- UNIT 2: Line-sanity!
- UNIT 3: Transformers and Transformations
- UNIT 4: Tremendous Triangles
- UNIT 5: Three Triangle Topics
- UNIT 6: Pretty Polygons
- UNIT 7: MidTerm Materials
- UNIT 8: Circles
- UNIT 9: 3-D Shapes and Volume
- UNIT 10: Sweet Similar Shapes
- UNIT 11: Trig Trickery
- UNIT 12: Finally Finals

- LESSON 1: Discovering Similar Triangles
- LESSON 2: More Discovering Similar Triangles
- LESSON 3: Transformations + Similarity
- LESSON 4: 2 Triangles in 1
- LESSON 5: Arabic Surveying Project
- LESSON 6: Proving Pythagoras' Theorem
- LESSON 7: Review Day for Sweet Similar Shapes
- LESSON 8: Assessment for Sweet Similar Shapes