Arrange 3 copies to prove interior angles of triangles

5 teachers like this lesson
Print Lesson


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.

Warm Up

10 minutes

Play of the Day

40 minutes


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.


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.