Answer: Choice D
{(-9,3), (8,7), (-9, -9), (2, 4)}
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Step-by-step explanation:
To find an example of a non-function, we look for (x,y) points where x repeats itself. That occurs in choice D where we have (-9,3) and (-9,-9) in the same function set.
The input x = -9 leads to multiple outputs y = 3 and y = -9 simultaneously. This is not allowed if we wanted a function.
A function is only possible if each input x leads to exactly one y output.
So this is why we look for repeated x values when trying to find non-functions. Choices A, B and C all have unique x values that don't repeat, which means those choices represent functions.
Side note: The y values can repeat, but the function won't be one-to-one.