Prove interior angles of triangles 2

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SWBAT prove that the sum of the interior angles of a triangle is 180 degrees.

Big Idea

Get kids fluent in proving this geometry fact.

Warm Up

10 minutes

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. Here is today's warmup: Prove interior angles of a triangle using transversal 2.

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

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?

I usually start with a stronger student, who sets the pace and inspires others with a stronger explanation.  The best presenters establish certain facts before diving into the proof, and we highlight that as students come up.  The better presenters also use the vocabulary fluently, another challenge for struggling students.  I usually do 3 students in each huddle for each class - 1 strong, 1 struggler, and 1 medium to knock it out of the park to end it.


15 minutes

Tonight's homework 7 - 6 HW96 Prove interior angle of triangles using transversals 2 should take about fifteen minutes.