Lesson objective: Solve systems of equations by first rewriting an equation in order to determine an equivalent expression.

This lesson helps to build procedural skill with using equations to solve systems. Equations are used here because they support representing relationships in abstract ways. This work develops students' understanding that systems can be solved by applying properties of equality to write and solve equations in one variable.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they reason about equations and use properties of equality to determine equivalent expressions that can be used to write and solve equations in one variable related to the system.

**Key vocabulary:**

- equivalent equation
- equivalent expression
- Properties of Equality
- Properties of Operation
- substitution