Math 1 · Unit 2 · Lesson 3 · part 2 of 6
Domain is the inputs, range is the outputs
A function is a rule with one output for each input.
Domain is the inputs, range is the outputs
A function is a rule with one output for each input. Now we name the two piles of numbers on either side of the rule. The domain is all the inputs the function is allowed to take: the x values. The range is all the outputs it gives back: the y values.
From a table
y = 2x + 1
| x | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| y | 3 | 5 | 7 | 9 |
Domain (the inputs): 1, 2, 3, 4.
Range (the outputs): 3, 5, 7, 9.
From a rule with no story
y = 2x + 1
If nothing stops you, you can feed in any number at all: 0.5, −37, a million. Then the domain (the inputs) is all numbers, and since the line goes on forever in both directions, the range (the outputs) is all numbers too.
A story changes that. Stories put limits on the inputs and the outputs, and that is the next section.
Two words, two piles. Domain: the inputs, the x values you are allowed to put in. Range: the outputs, the y values that come out. Say both words with their plain English every time until it is automatic.