8.32. Let R and S be rings. Under precisely what circumstances is ROS an integral domain?
8.32. Let R and S be rings. Under precisely what circumstances is ROS an integral domain?
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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Could you explain how to show 8.32 in detail? I also attached definitions and theorems in my textbook.

Transcribed Image Text:**8.28.** For each of the following rings, which elements are units? Which are zero divisors?
1. \( \mathbb{Z}_{18} \)
2. \( \mathbb{Z}_3 \oplus \mathbb{Z}_9 \)
**8.32.** Let \( R \) and \( S \) be rings. Under precisely what circumstances is \( R \oplus S \) an integral domain?
**8.33.** Let \( F \) be a field with subfields \( K \) and \( L \). Show that \( K \cap L \) is a subfield of \( F \). Extend this to show that the intersection of any collection of subfields is a subfield.
**8.34.** Let \( p \) be a prime and \( F \) a field with \( p^2 \) elements. Show that \( F \) cannot have more than one proper subfield.
![**Definition 8.8.** Let \( R \) be a commutative ring. Then a nonzero element \( a \in R \) is said to be a **zero divisor** if there exists a nonzero \( b \in R \) such that \( ab = 0 \).
**Example 8.19.** In \( \mathbb{Z}_6 \), we note that 4 is a zero divisor, as \( 4 \cdot 3 = 0 \). On the other hand, 5 is not a zero divisor.
**Example 8.20.** The ring of integers has no zero divisors.
**Definition 8.9.** An **integral domain** is a commutative ring \( R \) with identity \( 1 \neq 0 \) having no zero divisors.
**Example 8.21.** The rings \( \mathbb{Z}, \mathbb{Q}, \mathbb{R} \) and \( \mathbb{C} \) are all integral domains.
**Example 8.22.** The polynomial ring \( \mathbb{R}[x] \) is an integral domain. Indeed, we know that it is a commutative ring with identity. Also, if \( f(x) = a_0 + a_1x + \cdots + a_nx^n \) and \( g(x) = b_0 + b_1x + \cdots + b_mx^m \), with \( a_i, b_i \in R \) and \( a_n \neq 0 \neq b_m \), then the unique term of highest degree in \( f(x)g(x) \) is \( a_nb_mx^{m+n} \). As \( R \) is an integral domain, \( a_nb_m \neq 0 \). Thus, \( f(x)g(x) \) is not the zero polynomial.
**Example 8.23.** The rings \( \mathbb{Z}\mathbb{Z}, \mathbb{Z}_6 \) and \( M_2(\mathbb{R}) \) all fail to be integral domains. The first lacks an identity, the second has zero divisors and the third is not commutative.
**Theorem 8.7 (Cancellation Law).** Let \( R \](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fe15ed467-90ec-4e60-afef-3d3f6119f74d%2Fb4820b17-96cb-4b6c-a33a-0f499ddd7563%2Fur70rv6_processed.png&w=3840&q=75)
Transcribed Image Text:**Definition 8.8.** Let \( R \) be a commutative ring. Then a nonzero element \( a \in R \) is said to be a **zero divisor** if there exists a nonzero \( b \in R \) such that \( ab = 0 \).
**Example 8.19.** In \( \mathbb{Z}_6 \), we note that 4 is a zero divisor, as \( 4 \cdot 3 = 0 \). On the other hand, 5 is not a zero divisor.
**Example 8.20.** The ring of integers has no zero divisors.
**Definition 8.9.** An **integral domain** is a commutative ring \( R \) with identity \( 1 \neq 0 \) having no zero divisors.
**Example 8.21.** The rings \( \mathbb{Z}, \mathbb{Q}, \mathbb{R} \) and \( \mathbb{C} \) are all integral domains.
**Example 8.22.** The polynomial ring \( \mathbb{R}[x] \) is an integral domain. Indeed, we know that it is a commutative ring with identity. Also, if \( f(x) = a_0 + a_1x + \cdots + a_nx^n \) and \( g(x) = b_0 + b_1x + \cdots + b_mx^m \), with \( a_i, b_i \in R \) and \( a_n \neq 0 \neq b_m \), then the unique term of highest degree in \( f(x)g(x) \) is \( a_nb_mx^{m+n} \). As \( R \) is an integral domain, \( a_nb_m \neq 0 \). Thus, \( f(x)g(x) \) is not the zero polynomial.
**Example 8.23.** The rings \( \mathbb{Z}\mathbb{Z}, \mathbb{Z}_6 \) and \( M_2(\mathbb{R}) \) all fail to be integral domains. The first lacks an identity, the second has zero divisors and the third is not commutative.
**Theorem 8.7 (Cancellation Law).** Let \( R \
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