Solution
= Solution
The <ring of integers of a quadratic field> and its <field discriminant> are
$$
\boxed{
\begin{cases}
\{1,(1+\sqrt d)/2\},\quad D_K=d,&d\equiv1\pmod4,\\
\{1,\sqrt d\},\quad D_K=4d,&d\not\equiv1\pmod4.
\end{cases}}
$$
= Solution
The <ring of integers of a quadratic field> and its <field discriminant> are
$$
\boxed{
\begin{cases}
\{1,(1+\sqrt d)/2\},\quad D_K=d,&d\equiv1\pmod4,\\
\{1,\sqrt d\},\quad D_K=4d,&d\not\equiv1\pmod4.
\end{cases}}
$$