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Big Ideas:
Adding expressions is done by using any order, any grouping (commutative and associative properties), and then combining like terms.
There is no need for subtraction if you use the additive inverse.
The opposite of a sum is the sum of its opposites.
This lesson builds on students' prior work with combining like terms by using mathematical properties in 6.EE.A.4. In this lesson, students will add and subtract expressions with whole positive, negative, and rational numbers. Students will understand that in order to subtract they must use the additive inverse. The launch introduces a geometric context for adding and subtracting expressions. The task supports and extends their understanding of the 7.EE.A.1 standard by challenging students to determine the dimensions and perimeter of a frame to see if an award will fit in the frame. As a result, students add and subtract the sides, represented as expressions. Students must reason about the size of the frame and determine if the award fits. The mathematical concepts in this lesson build towards students' future work with solving equations in grades 7-8. It also provides a foundation for their work with adding and subtracting expressions of degree >1 in future grades.
Vocabulary: expression, additive inverse, term, coefficient, properties (commutative, associative, distributive)
Special Materials:
Algebra Tiles (optional)