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
Section: Chapter Questions
Problem 1RQ
icon
Related questions
Question
100%

Could you explain how to show 8.32 in detail? I also attached definitions and theorems in my textbook.

**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.
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 \
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 \
Expert Solution
trending now

Trending now

This is a popular solution!

steps

Step by step

Solved in 3 steps

Blurred answer
Knowledge Booster
Inequality
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, advanced-math and related others by exploring similar questions and additional content below.
Recommended textbooks for you
Advanced Engineering Mathematics
Advanced Engineering Mathematics
Advanced Math
ISBN:
9780470458365
Author:
Erwin Kreyszig
Publisher:
Wiley, John & Sons, Incorporated
Numerical Methods for Engineers
Numerical Methods for Engineers
Advanced Math
ISBN:
9780073397924
Author:
Steven C. Chapra Dr., Raymond P. Canale
Publisher:
McGraw-Hill Education
Introductory Mathematics for Engineering Applicat…
Introductory Mathematics for Engineering Applicat…
Advanced Math
ISBN:
9781118141809
Author:
Nathan Klingbeil
Publisher:
WILEY
Mathematics For Machine Technology
Mathematics For Machine Technology
Advanced Math
ISBN:
9781337798310
Author:
Peterson, John.
Publisher:
Cengage Learning,
Basic Technical Mathematics
Basic Technical Mathematics
Advanced Math
ISBN:
9780134437705
Author:
Washington
Publisher:
PEARSON
Topology
Topology
Advanced Math
ISBN:
9780134689517
Author:
Munkres, James R.
Publisher:
Pearson,