Lesson objective: Fluently multiply with negative numbers.

This lesson helps to build fluency with rational number multiplication. Students use their prior knowledge of properties and definitions to develop proofs of the rules for multiplying with negative numbers. This work develops students' understanding that the sign rules are not just arbitrary facts to be memorized; rather, they follow logically from prior knowledge.

Students engage in Mathematical Practice 6 (Attend to precision) as they clearly communicate their reasoning in proofs of the sign rules for multiplying with negative numbers. They name definitions and properties that support their work.

**Key vocabulary:**

- additive inverse
- distributive property
- opposite
- properties of equality

**Special materials needed:**