**What is the difference between a function and a relation:** A **function **is a relation between a set of inputs and a set of outputs. Each input is related to only one output.

For example, y = 2x + 1 is a function because for every input (x) there is only one output (y).

A **relation **is a set of inputs and outputs, but the inputs may have **multiple outputs**.

For example, {(2, 4), (2, 5)} is a relation because for the input 2, there are two outputs: 4 and 5.