# Elimination with 2 Column Notes

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## Objective

SWBAT solve a system of equations by using elimination and explain the steps that they take using correct terminology.

#### Big Idea

In this lesson students write 2-column notes as they work to increase retention of process and concepts.

## Warm up

10 minutes

I plan for this Warm up to take about 5 minutes to complete, and about 5 minutes to review with the students.  The two problems in the warm up are special cases of solving systems.

In today's Warmup I show how two special cases appear when applying algebraic methods to solve systems of equations:

• two parallel lines
• 2 alternative equations for the same line

I expect the students  to apply their prior knowledge of graphing solutions to systems of equations to these two problems. I build off of this warm up to review the 3 possible solutions to a system of linear equations.

I model how I will go over the warm up in the video below:

## 2 column notes

30 minutes

In this lesson 2-column notes are an instructional method for students to connect writing out the steps on solving a system of equations on the right, and showing the work done algebraically on the left. The Elimination worksheet has the steps needed to solve the system of linear combinations and the problems to be worked .  It is meant to help students retain the procedures and reasoning in solving a system of linear combinations by elimination.  I encourage students to paraphrase the steps in their own words.

When teaching elimination, I refer back to a simpler example of adding opposites to create a sum of 0.  I start with questioning, by asking students about simple sums of opposites:

What is 2 + -2, 3 + -3, 5 + -5?

Once students recognize the pattern that adding opposites creates a sum of 0, then we discuss how important it is to know multiplication facts to create those opposites.  Students' prior knowledge of multiplication will help them to decide what number to multiply by to create an opposite.  Students that struggle with creating opposites sometimes benefit by modeling division to identify the factor of the product needed to create an opposite.

I demonstrate how to use the 2-column notes with number 3 on the Steps to Elimination-worksheet before students begin the assignment because it is a system of equations that intersects at one point. I had not reviewed this type of problem with the students in this lesson yet.  I instruct students to write out the steps on the right side of the notes, and to solve the system of equations algebraically on the left side. I encourage the students to paraphrase using their own words, but I did provide the steps on the worksheet for lower level students who struggle with writing the steps.