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# Prove exterior angles of triangles 2

Lesson 8 of 9

## Objective: SWBAT prove facts about the exterior angles of a triangle.

*75 minutes*

#### Warm Up

*10 min*

Each day, students complete a warm-up that usually consists of spiraling the previous day's material, in addition to older material. Warm-up problems also sometimes extend lessons that students have encountered before to more unfamiliar contexts.

For a video narrative about how I structure each lesson, and how the warm-up fits in, click here.

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#### Huddle

*10 min*

Today is about getting more and more kids fluent in their ability to prove this fact, and so I ask a few kids to come up to the board to present proofs, and to get evaluated by their peers. We use two simple questions to evaluate:

1. Is the logic correct?

2. Is the presentation clear and understandable?

At this point, students are developing the habits of mind needed to be strong proof-writers. They establish certain facts, choose the logical and correct sequencing of each step, and make a strong conclusion based on their reasoning. We talk about these three elements as the three elements that form the basis of a strong proof.

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#### Homework

*15 min*

Homework 98 is to be completed at home and should take students approximately 15 minutes.

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- UNIT 1: FLUENCIES AND THE LANGUAGE OF ALGEBRA
- UNIT 2: SOLVING LINEAR EQUATIONS
- UNIT 3: INTRODUCTION TO FUNCTIONS
- UNIT 4: INTERPRETING AND COMPARING LINEAR FUNCTIONS
- UNIT 5: SYSTEMS OF LINEAR EQUATIONS
- UNIT 6: EXPONENTS AND SCIENTIFIC NOTATION
- UNIT 7: PARALLEL LINES, TRANSVERSALS, AND TRIANGLES
- UNIT 8: CONGRUENCE AND SIMILARITY THROUGH TRANSFORMATIONS
- UNIT 9: PATTERNS OF ASSOCIATION IN BIVARIATE DATA
- UNIT 10: SLOPE REVISITED
- UNIT 11: VOLUME OF CYLINDERS, CONES, AND SPHERES
- UNIT 12: POLYNOMIALS AND FACTORING
- UNIT 13: QUADRATIC FUNCTIONS

- LESSON 1: Special angle pairs
- LESSON 2: Transversals 1
- LESSON 3: Transversals 2
- LESSON 4: Practice transversals and blast from the past
- LESSON 5: Prove interior angles of a triangle using transversals
- LESSON 6: Prove interior angles of triangles 2
- LESSON 7: Prove exterior angles of triangle
- LESSON 8: Prove exterior angles of triangles 2
- LESSON 9: Arrange 3 copies to prove interior angles of triangles