A function is a relation that assigns exactly one value in the range to each value in the domain. To figure out what a domain and range are, we think of the domain as "x" in an ordered pair and range as "y".
When listing domains and ranges, you insert them into brackets. ({})
For example, suppose a graph has 2 columns, one labeled x, and the other labeled y. In the x column, we have the numbers 1, 2, 3, 4, and 5. In the y, we have 2, 4, 6, 8, and 10.
The question is, what is the domain and range?
The domain would be: {1, 2, 3, 4, 5}, and the range: {2, 4, 6, 8, 10}
When listing domains and functions, you want to list them in order and not repeat any numbers.
HOW DO YOU KNOW WHAT IS A FUNCTION AND WHAT ISN'T?
A function is only allowed one y for each x. So, if a set of ordered pairs is like this: (2,3), (3, 7), (6, 13), (2, 9), it is not a function because 2 has two y's.
To make this a little easier, there is a method called the "stupid pencil trick" where you graph out the coordinates on a graph, hold a pencil vertically over the graph, and see if any y's are on the same line.
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