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# Arrange 3 copies to prove interior angles of triangles

Lesson 9 of 9

## Objective: SWBAT demonstrate their mastery of unit on parallel lines, transversals, and triangles.

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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 push a few kids to come up to the board to present their proof, 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?

It's nice to end the unit with arranging 3 copies, because it actually is a bit easier than the other proofs and provides a nice sense of closure to the proof-writing. We engage in error analysis right away - is there anything wrong with this picture? - and also focus on using different types of triangles - equilateral, scalene, isosceles, right triangles, etc. -- to see how they each are governed by the same principle. Pretty powerful to get kids to see this.

In terms of error analysis, I often use a scalene triangle and put two of the same angles together with a third, which does not form a straight line. I ask a fairly "naked" question - what is going on here? - and I see where the discussion takes us.

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#### Homework

*15 min*

Tonight's homework is a take-home assessment. Assessment #13 Transversals and Triangles is to be completed at home.

I did a lot of take-home assessments in this school year, to save instructional days, particularly in light of missing 5 days from Hurricane Sandy. In the future, I would likely complete this assessment as an in-class assessment.

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##### Similar Lessons

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###### PTA (Parallel Lines, Transversals and Angles)

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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