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# Triangle Inequality Theorem

Lesson 9 of 14

## Objective: Students will be able to determine if three side lengths can form a triangle.

#### Launch

*10 min*

**Opener: **As students enter the room, they will immediately pick up and begin working on the opener – Instructional Strategy - Process for openers. This method of working and going over the opener lends itself to allow students to construct viable arguments and critique the reasoning of others, which is **mathematical practice 3**.

**Learning Target: **After completion of the opener, I will address the day’s learning targets to the students. For today’s lesson, the intended target is “I can determine whether three side lengths can form a triangle.” Students will jot the learning target down in their agendas (our version of a student planner, there is a place to write the learning target for every day).

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#### Summary + Homework

*5 min*

**Instructional Strategy - Table Discussion: **To summarize this lesson, I am going to ask that students have a table discussion on the question – Think about the angles across from each side of a triangle – just knowing the side lengths, you can order the angles from largest to smallest – figure out how. For this summary, I am going to have students discuss at their tables, and I am going to ask someone from each table to share out. After every one shares, I will address the right/wrong answers.

Homework: After the table discussion I will pass out the homework for the students to get started on. Eventhough the assignment is long, it should go quick!

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Awesome! Loved the inquiry structure of the lesson handout. Thank you!

| 8 months ago | Reply

Nice lesson and I might want to try it but where are the instructions regarding how I am to set up the straws? Thank you.

| 2 years ago | Reply

Loved this lesson! Really got my kids engaged. Thanks for all your terrific lessons!

| 2 years ago | Reply*expand comments*

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- UNIT 1: Introduction to Mathematical Practices
- UNIT 2: Proportional Reasoning
- UNIT 3: Percents
- UNIT 4: Operations with Rational Numbers
- UNIT 5: Expressions
- UNIT 6: Equations
- UNIT 7: Geometric Figures
- UNIT 8: Geometric Measurement
- UNIT 9: Probability
- UNIT 10: Statistics
- UNIT 11: Culminating Unit: End of Grade Review

- LESSON 1: Scale Drawings
- LESSON 2: Scale Drawings - Fluency Practice
- LESSON 3: Scale Factor
- LESSON 4: Scale Factor - Fluency Practice
- LESSON 5: Scale Drawings - Area and Perimeter
- LESSON 6: Scale Drawings Review
- LESSON 7: Scale Drawings Test
- LESSON 8: Geometric Drawings
- LESSON 9: Triangle Inequality Theorem
- LESSON 10: Angle Pairs
- LESSON 11: Interior Angles of a Triangle
- LESSON 12: All Angle Relationships - Fluency
- LESSON 13: Geometric Figures Review
- LESSON 14: Geometric Figures Test