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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
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
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.