Lesson 5: Elimination Method
Duration of Days: 2
Lesson Objective
Students will solve systems of two linear equations in two variables algebraically using the elimination method.
Students will learn to add or subtract equations to eliminate a variable and use multiplication to create additive inverses.
How can we "get rid" of a variable by combining two equations?
When is it more efficient to use elimination rather than substitution or graphing?
Why is it necessary to multiply an entire equation by a constant before adding it to another?
Elimination, Addition Property of Equality, Multiplicative Property of Equality, Opposite Coefficients, Additive Inverse, Standard Form (Ax+By=C).
8.EE.C.8b: Solve systems of two linear equations in two variables algebraically, and estimate solutions by graphing the equations.
8.EE.C.8c: Solve real-world and mathematical problems leading to two linear equations in two variables.
Purpose: To provide students with an algebraic method for solving systems that are already in standard form or where substitution would result in complex fractions.
DOK Level: 2 (Skill/Concept) and 3 (Strategic Thinking).
Subtraction Errors: When subtracting equations, students often forget to distribute the negative sign to every term in the second equation.
Incomplete Multiplication: Students may multiply the variable terms but forget to multiply the constant.
Standard Form Alignment: Attempting to eliminate variables when equations are not aligned.
Use vertical alignment templates to help students keep variables and constants in neat columns.
Provide a "Choosing Your Method" flow chart to help students decide whether to add, subtract, or multiply first.
Offer "clue cards" that suggest which variable is easier to eliminate in a given system.
Exit Ticket
Performance Task