Prove interior angles of a triangle using transversals

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SWBAT prove that the interior angles of a triangle sum to 180 degrees, using transversals.

Big Idea

Get kids to prove facts using transversals. This is harder than it sounds!

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. Today's warmup can be found in 7 - 5 WU95.

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

I push kids to come up to the board to prove that the interior angles of a triangle is 180 degrees, using transversals. I have include two student proofs on video below and a third can be seen see students actually doing this on video. The Student Work file contains several examples of the students' written proofs. 

Student Proof #1


Student Proof #2




15 minutes

Homework 7 - 5 HW95 is to be completed at home and should take students approximately 15 minutes.