here the point x=-1 is mapped a first time into the point y= -2, and it is mapped a second time into the point y= 7. Now That can not possible for a function, so in order to get a function, we can write, for example, your relation, as follows:

{(-5, -4), (-2, -9), (-1, 2), (k, 7)}

where, of course k is a rela number different from -1

Mar 10th, 2015

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