Let $I$ be any ideal of $\mathbb {Z}[x]$, and $I=\left<{f_1,f_2 , ...}\right>$.
Without loss of generality, $f_1$ has minimal (absolute value) coefficient of constant term (if there exist).
Then, let $g$ be any element of $I$ .
We have for some integer $m$ that $g - mf_1$ is element of $I$ (minimal coefficient and division algorithm).
I guess this process terminate finitely, but I don't know how can I do next step.
( ex. $g-mf_1, g-mf_1-nf_2, ...$)
Please help me and thanks for in advance.
$\mathbb Z$ is Noetherian, and by Hilbert's basis theorem, so is $\mathbb Z[x].$ Therefore, by definition, all its ideals are finitely generated.