# Lesson 12

Functions with Multiple Parts

These materials, when encountered before Algebra 1, Unit 4, Lesson 12 support success in that lesson.

### Lesson Narrative

In this lesson, students examine the importance of using the domain in a description of a situation where different things are happening. Students encounter situations that encourage them to be precise about interval boundaries and then describe a graph using the domain. In the associated Algebra 1 lesson students look at piecewise functions including using the function notation to describe the domain of different pieces of a function.

Students must reason abstractly and quantitatively (MP2) when they interpret descriptions of events as piecewise functions. Looking for and making use of structure (MP7) is also essential when defining parts of the domain for which a piece of the function applies.

### Learning Goals

Teacher Facing

- Describe a situation based on a piecewise graph including domains in the description.
- Use a basic step function to compute sums of function values.

### Student Facing

- Let’s look at domains that have boundaries.

### CCSS Standards

Building Towards

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