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# Elimination 3 - multiply one equation only

Lesson 9 of 19

## Objective: SWBAT solve linear systems of equations using elimination, Day 3.

#### Warm-up

*10 min*

The Lesson 5 - 9 Warmup challenges students to use reasoning, rather than process to understanding the solution to a system of equations. The task asks the students to identify the correct partner equation to form a system with a given solution.

I like this task because it pushes kids to figure out a more efficient way to solve the problem, one that requires a deeper understanding of what a solution to a system of linear equations actually is. It is NOT efficient to solve each system (four times) to determine if the point (4, -5) is a solution. Rather, if kids understand that solutions make each of the equations true, all a student has to do is substitute in the coordinates into each equation to determine which one is the correct equation.

I further throw the kids by giving them a ton of space. This "tricks" them into thinking that this question requires a ton of work... I emphasize that they should not be robots, and should always think before they tackle a problem with a set of procedures.

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

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#### Homework

*15 min*

HW68 Elimination 3 - multiply one equation only includes 5 problems. Four are related to this lesson, one is spiraled review. I also give the kids the answers to the problems.

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- UNIT 1: FLUENCIES AND THE LANGUAGE OF ALGEBRA
- UNIT 2: SOLVING LINEAR EQUATIONS
- UNIT 3: INTRODUCTION TO FUNCTIONS
- UNIT 4: INTERPRETING AND COMPARING LINEAR FUNCTIONS
- UNIT 5: SYSTEMS OF LINEAR EQUATIONS
- UNIT 6: EXPONENTS AND SCIENTIFIC NOTATION
- UNIT 7: PARALLEL LINES, TRANSVERSALS, AND TRIANGLES
- UNIT 8: CONGRUENCE AND SIMILARITY THROUGH TRANSFORMATIONS
- UNIT 9: PATTERNS OF ASSOCIATION IN BIVARIATE DATA
- UNIT 10: SLOPE REVISITED
- UNIT 11: VOLUME OF CYLINDERS, CONES, AND SPHERES
- UNIT 12: POLYNOMIALS AND FACTORING
- UNIT 13: QUADRATIC FUNCTIONS

- LESSON 1: Solve systems of linear functions by graphing - TWO lines on the same graph?!?
- LESSON 2: Solve systems of linear equations by graphing - with some real-life applications
- LESSON 3: SUB! How can we use the properties of algebra to figure out the intersection of two lines WITHOUT graphing? (Day 1 of 3)
- LESSON 4: SUB! How can we use the properties of algebra to figure out the intersection of two lines WITHOUT graphing? (Day 2 of 3)
- LESSON 5: SUB! How can we use the properties of algebra to figure out the intersection of two lines WITHOUT graphing? (Day 3 of 3)
- LESSON 6: Assessment #9
- LESSON 7: Elimination 1 - add or subtract only
- LESSON 8: Elimination 2 - add or subtract only
- LESSON 9: Elimination 3 - multiply one equation only
- LESSON 10: Elimination 4 - multiply one equation only
- LESSON 11: Elimination 5 - mulitply both equations
- LESSON 12: Choose the best method to solve systems of equations
- LESSON 13: Real-life Systems 1
- LESSON 14: Real-life Systems 2
- LESSON 15: Real-life Systems 3 - Easy Price
- LESSON 16: Real-life Systems 4 - Sum Plus One Other
- LESSON 17: Real-life Systems 5 - Price-Sum Plus One Other
- LESSON 18: Mixed Review of Systems of Equations
- LESSON 19: Assessment #10 - Systems Unit Assessment