Prove that the set of all rational numbers of the form m/n, where m, n E Z and n is square- free, is a subgroup of Q (under +).

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Problem Statement:**

Prove that the set of all rational numbers of the form \( m/n \), where \( m, n \in \mathbb{Z} \) and \( n \) is square-free, is a subgroup of \( \mathbb{Q} \) (under \( + \)).

**Explanation:**

The problem asks us to demonstrate that a specific subset of rational numbers forms a subgroup. In group theory, a subgroup must satisfy three criteria under its operation (in this case, addition):

1. **Closure:** If \( a \) and \( b \) are elements of the set, then \( a + b \) must also be an element of the set.
2. **Identity:** The set must contain the identity element of the larger group. For rational numbers (under addition), the identity element is 0.
3. **Inverses:** For every element \( a \) in the set, there must be an element \( b \) in the set such that \( a + b = 0 \).

The challenge is to show that rational numbers of the form \( m/n \), where \( n \) is square-free (a number not divisible by any perfect square other than 1), satisfy these subgroup criteria within \( \mathbb{Q} \).
Transcribed Image Text:**Problem Statement:** Prove that the set of all rational numbers of the form \( m/n \), where \( m, n \in \mathbb{Z} \) and \( n \) is square-free, is a subgroup of \( \mathbb{Q} \) (under \( + \)). **Explanation:** The problem asks us to demonstrate that a specific subset of rational numbers forms a subgroup. In group theory, a subgroup must satisfy three criteria under its operation (in this case, addition): 1. **Closure:** If \( a \) and \( b \) are elements of the set, then \( a + b \) must also be an element of the set. 2. **Identity:** The set must contain the identity element of the larger group. For rational numbers (under addition), the identity element is 0. 3. **Inverses:** For every element \( a \) in the set, there must be an element \( b \) in the set such that \( a + b = 0 \). The challenge is to show that rational numbers of the form \( m/n \), where \( n \) is square-free (a number not divisible by any perfect square other than 1), satisfy these subgroup criteria within \( \mathbb{Q} \).
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