Angles and Algebra

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SWBAT use algebra to model relationships involving angles and apply techniques to solve equations.

Big Idea

Using algebraic expressions for angles reinforces student understanding of basic algebra tools.

Lesson Introduction

15 minutes

I start this lesson by reviewing problems from the previous lesson on triangle angle sums. I often review the problems if a class was short on time and I always review the triangle sum proof, because it is something I want them to take with them in all their angle investigations.  

Then I give them a few sample angle algebra problems before they spend time with their partner working on the problem set for the lesson

Here is a cache of lesson resources that I use to open today's lesson: algebra intro.pptx.

Problem Set

30 minutes

For this portion of the lesson, I encourage students to work in partnerships on a collection of algebra angle problems that I downloaded from the website The site was designed specifically for New York State Regent's exams, but they can be used for any curriculum. The problem sets are great and worksheets are easy to download in bundles.

I like to give each partnership an Angles and Algebra sheet and I put the answers in two sections of the room. I ask students to get up and check their answers every 5 problems or so to mark their progress. This helps them identify a misconception without my help. I find that this strategy helps students avoid moving through a whole set of problems without recognizing that their ideas aren't exactly working out. 

Worksheet with answer keyangles and algebra with answers.pdf


15 minutes

During the partner work I circulate. I highlight and make note of especially useful errors and ideas. During the summary I write these down and use them to encourage class discussion. I use a presentation of the problems from the algebra problem set to focus the class's attention. 

The summary discussion goes beyond just showing solutions to problems. Instead, we are either affirming or refuting ideas that students applied during the lesson. If there are problems that most students struggle with, we start by reviewing those. I try to discuss what students found difficult and see how others would suggest they overcome that obstacle.