# Math Help - Functions

1. ## Functions

How this one a function

{[ -2,-1), (-1,0), (0,1), (1,2) (2,2)}

but this one isnt

{(-4,1), (-2,1), (-2,0)

I thought functions cant have the same number appearing more than once in a relation?

2. ## Re: Functions

a relation is a function if all ordered pairs have different first elements,but second can be the same.

3. ## Re: Functions

What's the definition of a function? ...

EDIT:
Anonimnystefy has given the defintion, but to be more exact, if you have given a functon $f:A \to B$ then:
$\forall a \in A, \exists! b\in B: (a,b)\in f$