Question 141525
If any value of x results in two or more values for f(x), then f is NOT a function.


Graphically, that means that if you can find a vertical line that intersects the graph of the relation in two or more points, the relation is not a function.


It doesn't matter if more than one value of x results in the same value for f(x) -- the relation is still a function


In sum, if each x maps to exactly one value of f(x), even if more than one x maps to a given f(x), you have a function.  If any x maps to more than one value of f(x), you don't have a function.