For what value of c is the relation a function? start set open paren 2 comma 8 close paren comma open paren 12 comma 3 close paren comma open paren c comma 4 close paren comma open paren negative 1 comma 8 close paren comma open paren 0 comma 3 close paren end set

A relation is a function if each input (the first coordinate) has only one output. The existing inputs are 2, 12, −1, and 0, so c cannot equal any of those values because (c, 4) would give that input a different output. Of the choices, only 1 is not already an input, so the correct choice is C, 1.

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