Below are tables for two functions, $f$ and $g\text{.}$ The function $f$ is invertible, but the function $g$ is non-invertible.
 Invertible function $f$ Non-invertible function $g$ $x$ $f(x)$ $x$ $g(x)$ $-3$ $6$ $5$ $-9$ $-1$ $-3$ $2$ $4$ $2$ $-1$ $-1$ $-9$ $4$ $0$ $3$ $5$
In the last problem, you decided why a certain table was non-invertible.
In general, a function is non-invertible if:
In general, a function is invertible if:

Hint: