Question 375088
{ (1, -5), (2, -4), (10, 0), (11, -1), (13, -4), (19, 9), (2, -5)}.  This relation is NOT a function, because of the points (2, -4) and (2, -5).  For a function, no single value of an independent variable can be associated with more than one value of the dependent variable.