Lesson objective: Identify equivalent expressions by substituting values in place of the variable.

This lesson helps to build procedural skill with evaluating expressions for a given value. Substitution is used here because it highlights that different expressions can have the same value for one value of the variable but that doesn't make the expressions equivalent. This work develops students' understanding that equivalent expressions have the same value regardless of what value is used in place of the variable.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they evaluate expressions at multiple values of the variable to understand the abstract concept of equivalency. Students will recognize that having the same value for one value of the variable does not mean two expressions are equivalent.

**Key vocabulary:**

- evaluating an expression
- equivalent expressions
- substitution