Lesson objective: Understand that a function pairs each input with exactly one output.

Students bring prior knowledge of relationships between variables from 6.EE.C.9. This prior knowledge is extended to functions as students recognize how inputs and outputs pair together to form a function. A conceptual challenge students may encounter is understanding that only the input values have to be unique in a relation in order for it to be a function.

The concept is developed through work with codes represented in words, as a mapping, and as a table, which helps students visualize the input/output pairs they will examine to define a function.

This work helps students deepen their understanding of numbers and equivalence because of how the input values and output values relate to each other as they are represented in multiple ways.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) and Mathematical Practice 4 (model with mathematics) as they identify how input and output values are paired together in different forms, and whether those pairs help to define a function or not.

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