Question 51652
In mathematics, a function is a relation, such that each element of a set (x values)(the domain) is associated with a unique element of another(y value) (possibly the same) set (the codomain, not to be confused with the range). 
---definition---
So here we can obviously figure out some points

       1. there can be one or more members in the set of Domain(X values), associate(make connection) to a unique value( one value) in the set of range(Y values.

      2. But there can not be one value in the set X associates to two or more values in the set of Range(Y values). 


For Eg:-    if    f(2) = 12 
                  f(9) = 12

                          so f is a function, which satisfies the definition

         but if  f(6) = 5
                 f(6) = -10
                         is not a function.


So in your case,
(2,2), (1,4), (3,6), (-1,2)

You can find this a function as every element in the set of X associates with the unique value of Y

but if Your co-ordinates are like the following,
(2,2), (1,4), (3,6), (2,6)

See the first & last co ordinate (2,2)(2,6) , so here for the element 2 in the set of X associates with two different values of Y. so its not a funtion.


Domain- the set of the X values ,that can be satisfy the funtion.
Range- Set of Y values,that associate with the values, according to the funtion.

In your case Domain is could be all the real numbers and Range also all the real numbers