What are Domains and Ranges?
In the illustration above, the set of all input numbers into a function is called the domain. And the set of all output numbers from a function is called the range.

Let's take a look at a more concrete example
Consider a set of ordered pairs {(2,5), (3,8), (4,12), (6,-12)} What is the domain and range for the set of ordered pairs above? The domain for the above set of ordered pairs is {2, 3, 4, 6}.

The range for the above set of ordered pairs is {5, 8, 12, -12}.

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A few simple facts that you should know

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Did you notice that the domain is the set of all possible first component values in the set of ordered pairs? And did you notice that the range is the set of all second component values that can result from using values in the domain?


Why do we need domains and ranges?

Domains and ranges are important ideas that will help us to understand the relationship between two variables in an equation, especially when we begin graphing. The concept of domains and ranges will re-emphasize points made in the linear and graphing functions stations.