Question

How do I know if it's a function or not?

Answer 1

in plain and short, a function has no x-coordinate Repeats, if there's an x-coordinate Repeat, then is not a function.

$\bf \begin{array}{ccll} x&y\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 6&3\\ 8&2\\ 9&0\\ \stackrel{re peat}{11}&1\\ \stackrel{re peat}{11}&2 \end{array}$

Answer 2

your domain would be (6,8,9,11,11)
your range would be (3,2,0,1,2)
This is not a function because the domain 11 is paired with both the range of 1 and 2