# Exponential Functions

Allowance day—time to go buy that new video game / pair of jeans / crazy gadget. Wait, what's that, Mom? You want me to save *all* of my allowance now? Lame.

Every week you put away money, watching the number tick up at the same rate: $15, $30, $45. This change can be easily represented by the linear function 15*x*, assuming *x* represents weeks.

A linear function's got a constant rate of change. In other words, you *add* the same amount for every increase in *x*. Here you're adding $15 per week to your account, or for every increase in *x*, you *add* 15.