Lesson 3
Lots of Rectangles
These materials, when encountered before Algebra 1, Unit 6, Lesson 3 support success in that lesson.
Lesson Narrative
In previous grades, students used the areas of partitioned rectangles to make sense of the distributive property, which also involves making sense of combining like terms. In the associated Algebra 1 lesson, students will write expressions to describe how a visual pattern is growing. This work relies on being able to efficiently express the area of a figure. In order to express the area of a rectangle, you need to be able to express the lengths of its sides. This lesson provides a geometric foundation for making sense of both the distributive property and combining like terms. Additionally, it refamiliarizes students with the idea of expressing the same area in different ways. When students write areas of rectangles in different but equivalent forms, they are noticing and making use of structure (MP7).
Learning Goals
Teacher Facing
 Revisit the geometric basis for the distributive property and combining like terms.
 Write equivalent expressions to represent the areas of rectangles.
Student Facing
 Let’s express the areas of some rectangles.
CCSS Standards
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