Example for a function:

If you have this set of plot points/ordered pairs,

{(1,2), (3,4), (5,6)}

Does each input number/first number in the pair (domain), have only one corresponding output number (range) to the second number in the pair?

The domain numbers/values are {1,3,5}.

The range numbers/values are {2,4,6}.

The answer is yes. The domain values have only one range value, so it is a function.

Example of NOT a function:

If you have this set of plot points/ordered pairs –

{(1,2), (1,4), (5,6)

Does each input/first number (domain) have only one corresponding output number (range) in the pair?

The domain values are {1,1,5}.

The range values are {2,4,6}.

It is NOT a function. The domain values DO NOT HAVE ONLY ONE range value. Two of the ordered pairs have a domain of 1 with a different range value, so it is not a function.

Hope this helps.