( - ∞, 3) ∪ (3, ∞ )
The domain is the set of values of x which make f(x) defined
The denominator of f(x) cannot be zero as this would make f(x) undefined. Equating the denominator to zero and solving gives the value that x cannot be.
solve x - 3 = 0 ⇒ x = 3
domain : (- ∞, 3) ∪ (3, ∞ )
