For a relation to be considered a function, each input value must correspond to exactly one output value. This means that for every value you put into the function (often called the "input" or "domain"), there should be one and only one value that comes out (often called the "output" or "range"). If any input value leads to more than one output, then the relation is not a function.

Would you like more details or have any questions?

Here are 5 related questions you might find helpful:

1. What is the difference between a function and a relation?
2. How can you determine if a graph represents a function?
3. What is the vertical line test, and how does it relate to functions?
4. Can a function have the same output for different inputs? Why or why not?
5. How are domain and range defined in the context of functions?

Tip: A simple way to test if a relation is a function is to check if every input value maps to a single output value.