Question

What is a function and not a function?

Answer 1

Relation

• A relation is a relationship between input values and output values.

Function

• A function is a relation if and only if there is a unique co-domain value for every domain value.
• The input is called a domain and the output is called a range.
• All input values must have one output value.
• Example:
  

Not a function:

• In relation, if we get more than one output for input, then the function is not a relation.
• There will be multiple or no values in the co-domain for every domain value.
• Example: