How can you use a mapping diagram to determine the domain and the range of a relation?

Step 1: Draw the mapping diagram for the given relation.
Step 2: A relation is a function if each element in the domain is paired with one and only one element in the range.
Step 3: From the mapping diagram, it can be observed that the given relation is not a function as '3' in the domain is paired with two elements - 1 and - 2 in the range and '6' is paired with - 1 and - 2.

                              Domain                Range 
                                        3         |     -1
                                                   |
                                                   |
                                        6         |     -2

The vertex of the quadratic function is (1.5, -.75)