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# What is a Function?

Lesson 1 of 10

## Objective: SWBAT identify functions from ordered pairs, a table, a graph, and a mapping diagram.

#### Resources

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To introduce the idea of a function I will act out the following narrative while Slide 3 of Functions is showing:

**One day I was walking down the street and I decided that I was really thirsty. I saw a soda machine and pulled out a dollar to get something to drink.**

At this point I will tap on the board to simulate getting a soda out of the machine, and I will ask students to make and fill in the blank input/output table at the top of their notes. The input will be the button that I push, and the output is the corresponding table:

** Input Output**

Coke Button --> Coke Can

Coke Button --> Coke Can

Sprite Button --> Sprite Can

Coke Button --> Coke Can

I will ask students to to turn-and-talk to their neighbor for about 30 seconds about what happened in my simulation. I will ask students if anything strange happened, and to decide if the machine is **functioning****.**

Next, I will proceed to the soda machine on Slide 4. I will also tell students a similar narrative about wanting a beverage to drink, and I will ask students to fill in the second input/output table for this new machine:

** Input Output**

Coke Button --> Coke Can

Coke Button --> Sprite Can

Sprite Button --> Root Beer Can

Coke Button --> Water Bottle

Again, I will ask students to turn-and-talk to their neighbor about what happened in this simulation. I will ask students if anything strange happened, and to decide if this machine is **functioning**. I will also ask students to describe the relationship between the inputs and outputs in both machines, and how the the presence of a repeating input or output affected whether or not the machine functioned correctly.

Finally, I will show students the tables on next slide, and invite students to create their own definition of the word function. After a brief discussion and examination of about functions and non-functions, I will introduce the vertical line test as a way to classify functions on a graph. I will ask students to use what they know about functions to explain why the vertical line test works.

Students will follow along with this lesson using Guided Notes.

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#### Partner Practice: Card Sort

*30 min*

Students will work in pairs to complete the Function Card Sort Activity. Pairs will first cut up the cards. Next, students will sort the cards into two groups (Function/Not a Function) and glue the card onto the corresponding side. Lastly, students will write a sentence on page two justifying their response using math terminology.

After about 20 minutes, we will reconvene as a whole group and compare our responses. I will ask students to share their examples of functions that they created on their own.

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#### Resources

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- UNIT 1: Welcome Back! - The First Week of School
- UNIT 2: Linear & Absolute Value Functions
- UNIT 3: Numeracy
- UNIT 4: Linear Equations
- UNIT 5: Graphing Linear Functions
- UNIT 6: Systems of Linear Equations
- UNIT 7: Linear Inequalities
- UNIT 8: Polynomials
- UNIT 9: Quadratics
- UNIT 10: Bridge to 10th Grade

- LESSON 1: What is a Function?
- LESSON 2: Domain and Range
- LESSON 3: Function Notation
- LESSON 4: Writing Linear Equations (Day 1 of 2)
- LESSON 5: Writing Linear Functions (Day 2 of 2)
- LESSON 6: Slope & Rate of Change
- LESSON 7: Graphing Linear Functions (Day 1 of 2)
- LESSON 8: Graphing Linear Functions (Day 2 of 2)
- LESSON 9: Graphing Absolute Value Functions (Day 1 of 2)
- LESSON 10: Graphing Absolute Value Functions (Day 2 of 2)