Question

For a relation to be a function what must never happen

Answer 1

each input (x-value) only has one output (y-value)

Explanation:

you can use the vertical line test; pretend to draw vertical lines and if there are two point on the graph where the vertical line touches, it cannot be considered function.

Answer 2

Explanation:

A function is a relation in which each input has only one output

so a relation cannot have more than one output