Principal Ideal from Element in Center of Ring
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Theorem
Let $\struct {R, +, \circ}$ be a ring with unity whose zero is $0_R$ and whose unity is $1_R$.
Let $b \in R$ be in the center of $R$.
Then:
- $\ideal b = R \circ b = \set {x \circ b: x \in R}$
where $\ideal b$ is the principal ideal generated by $b$.
Proof
Let $J = R \circ b$
The center of $R$ is defined as:
- $\map Z R = \set {x \in R: \forall s \in R: s \circ x = x \circ s}$
Therefore:
- $R \circ b = b \circ R = \set {x \circ b: x \in R} = \set {b \circ x: x \in R}$
and so:
- $x \in J \implies x \circ b \in J \land b \circ x \in J$
Thus $J$ is an ideal of $R$ and so $J = \ideal b$.
$\blacksquare$
Sources
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $\text {IV}$: Rings and Fields: $22$. New Rings from Old: Theorem $22.5$