# Arrange 3 copies to prove interior angles of triangles

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## Objective

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

#### Big Idea

Get performance data on student mastery of this unit by assessing students on key concepts and practices.

10 minutes

40 minutes

## Huddle

10 minutes

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.

## Homework

15 minutes

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.