1. Introduction

2. Welcome to What is x?

Activity 1: What is x?

Practice 1: Naming Collections Round 1

Practice 2: Naming Collections Round 2

3. Substitution

Activity 2: Substitution

Practice 3: Substitution

Activity 3: Showing that x + x = 2

Practice 4: Advanced Naming Collections

4. Solving for x

Activity 4: Solving for x

Practice 5: Solving Equations

5. Functions

Activity 5: Functions

Practice 6: Functions

Activity 6: Function Machines

Function Machine 1

Function Machine 2

Function Machine 3

Function Machine 4

Function Machine 5

Function Machine 6

Function Machine 7

Function Machine 8

Function Machine 9

6. Solutions/Answers

7. Help for Helpers (Parents and Teachers)

### What is x?

The learning objectives in each of the lessons are these:

- What is x ?: The abstract concept of variable is introduced.
- Substitution: The idea that a number can be exchanged for a variable is introduced.
- Showing that x + x = 2 : Algebraic expressions like “2 ” make complete sense to those of us who have done algebra for years. But understanding that an expression like this means “2 multiplied by ” is not always obvious.
- Solving for x: This is where students solve the first set of actual problems. Actually solving reasonably complicated equations with reliability and confidence feels good!
- Functions: These exercises/problems build confidence in the principles in the prior lessons. And problems like these appear on all sorts of state and other tests—now your student has a chance to solve them, when he or she may not have been able to do so before. But that is not the goal of this lesson, just a positive consequence.

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