The domain is the set from which the function "starts", i.e. it is the set of the inputs you feed the function with.
In this case, the function starts from the set [tex]\{-2, 2, 3, 4\}[/tex] and lands on the set [tex]\{3, 9, 12\}[/tex]
So, the domain is the set [tex]\{-2, 2, 3, 4\}[/tex].
