Jeff Li MTP KIPP Infinity Charter School, NEW YORK, NY
8th Grade Math : Unit #7 - PARALLEL LINES, TRANSVERSALS, AND TRIANGLES : Lesson #5

# Prove interior angles of a triangle using transversals

Objective: SWBAT prove that the interior angles of a triangle sum to 180 degrees, using transversals.
Standards: 8.G.A.5 MP1 MP2 MP3 MP7
Subject(s): Math
60 minutes
1 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.

resources
2 Play of the Day - 40 minutes
7 - 5 VN95 Prove interior angles of triangles using transversals.MOV
https://betterlesson.com/lesson/section/6261/prove-interior-angles-of-a-triangle-using-transversals
resources
7 - 5 POTD95 Prove angle sum and exterior angles of a triangle using transversals.docx.doc.pdf
https://betterlesson.com/lesson/resource/2032922/7-5-potd95-prove-angle-sum-and-exterior-angles-of-a-triangle-using-transversals-pdf
7 - 5 POTD95 Prove angle sum and exterior angles of a triangle using transversals.docx.doc.docx
https://betterlesson.com/lesson/resource/2015717/7-5-potd95-prove-angle-sum-and-exterior-angles-of-a-triangle-using-transversals-docx
3 Huddle - 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

resources
4 Homework - 15 minutes

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