I believe this is...
You probably already know that a numerator cannot equal zero.
So let's work with 0≠x2-4
0≠x-2 and 0≠x+2
x≠2 and 0≠-2
The domain is all integers except -2 and 2.
According to Michael F., the Wyant of Wilton, CT, "the parentheses ( and ) indicate no endpoints. The symbol ∪ means set union."