Answer:
x ∈ R, x ≠ 1
Explanation:
f(g(x))
= f(
)
=

=

=

=

The denominator of f(g(x)) cannot be zero as this would make f(g(x)) undefined. Equating the denominator to zero and solving gives the value that x cannot be, that is
4x - 4 = 0 ⇒ 4x = 4 ⇒ x = 1 ← excluded value
Domain : x ∈ R, x ≠ 1, that is
(- ∞, 1) ∪ (1, ∞ ) ← in interval notation