Evaluation at i
Let
- Prove that
. - Prove that
is a maximal ideal in .
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Let $\varepsilon:{\bf R}[x]\to {\bf C}$ be the ring homomorphism that is evaluation at $i$, so $\varepsilon(f)=f(i)$. (Here $i$ denotes the complex number sometimes denoted $\sqrt{-1}$.)
\begin{enumerate}[label=\alph*)]
\item Prove that $\ker(\varepsilon)=(x^2+1)\subseteq {\bf R}[x]$.
\item Prove that $(x^2+1)$ is a maximal ideal in ${\bf R}[x]$.
\end{enumerate}