Exercise 111.24.3. Let $A$ be a ring. Let $B = A[x]$ be the polynomial algebra in one variable over $A$. Let $f = a_0 + a_1 x + \ldots + a_ r x^ r \in B = A[x]$. Prove carefully that the image of $D(f)$ in $\mathop{\mathrm{Spec}}(A)$ is equal to $D(a_0) \cup \ldots \cup D(a_ r)$.

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