Question

Determine if this is a function.

Answer 1

Answer: This is not a function

Why not?

The input x = 2 leads to more than one output. In this case, it leads to y = 20 and y = 40 simultaneously. This is the reason why we don't have a function. A function is only possible if each input x leads to exactly one y output.

Put another way: we cannot have x repeating any values if we want a function.

Side note: We could have y repeat however. So it's possible to have a function with the two points (1,5) and (3,5).