In this opening lesson, students recall the meaning of functions (which was introduced in grade 8) and encounter examples of functions and their representations in context. They use tables and graphs that represent relationships to determine whether the relationships are functions or not. Students are also reminded of the meaning of points on a graph as an input-output pair for a function and its meaning in the context of a real-life situation.

Students define a function as a relationship that takes inputs from one set and assigns them to outputs from another set, assigning exactly one output to each input. They also define an independent variable as the input of a function and a dependent variable as the output of a function.

Students practice making sense of problems and persevering in solving them (MP1) as they look for and explain correspondences between verbal descriptions, tables, and graphs. They engage in aspects of modeling (MP4) as they identify input and output variables in real-life situations and create representations of their relationships.