# Lesson 10

Piecewise Linear Functions

Let’s explore functions built out of linear pieces.

### 10.1: Notice and Wonder: Lines on Dots

What do you notice? What do you wonder?

### 10.2: Modeling Recycling

- Approximate the percentage recycled each year with a piecewise linear function by drawing between three and five line segments to approximate the graph.
- Find the slope for each piece. What do these slopes tell you?

### 10.3: Dog Bath

Elena filled up the tub and gave her dog a bath. Then she let the water out of the tub.

- The graph shows the amount of water in the tub, in gallons, as a function of time, in minutes. Add labels to the graph to show this.
- When did she turn off the water faucet?
- How much water was in the tub when she bathed her dog?
- How long did it take for the tub to drain completely?
- At what rate did the faucet fill the tub?
- At what rate did the water drain from the tub?

### 10.4: Distance and Speed

The graph shows the speed of a car as a function of time. Describe what a person watching the car would see.

The graph models the speed of a car over a function of time during a

3-hour trip. How far did the car go over the course of the trip?

There is a nice way to visualize this quantity in terms of the graph. Can you find it?

### Summary

This graph shows Andre biking to his friend’s house where he hangs out for a while. Then they bike together to the store to buy some groceries before racing back to Andre’s house for a movie night. Each line segment in the graph represents a different part of Andre’s travels.

This is an example of a piecewise linear function, which is a function whose graph is pieced together out of line segments. It can be used to model situations in which a quantity changes at a constant rate for a while, then switches to a different constant rate.

We can use piecewise functions to represent stories, or we can use them to model actual data. In the second example, temperature recordings at several times throughout a day are modeled with a piecewise function made up of two line segments. Which line segment do you think does the best job of modeling the data?