Which set is defined as Q(2)={a+b2∣a,b∈Q}\mathbb{Q}(\sqrt{2}) = \{ a + b\sqrt{2} \mid a, b \in \mathbb{Q} \}Q(2)={a+b2∣a,b∈Q}?
A quadratic field
A ring of integers
The set of all irrationals
A non-Archimedean field