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What's a Function (Intro to Domain and Range)

Let's try a box with some numbers in it:

THE RULE:  Add 1

input -> rule: +1 -> output
 

What can we put in this box?

input: 3 -> rule: + 1 -> output: 4 ... input: pi -> rule: + 1 -> output: pi + 1
 

We can put anything in this box -- even goofy irrational numbers like pi!  So...

domain  =  all real numbers

   range  =  all real numbers