If Q(x) is the statement x + 1 > 2x, and the domain is the set of positive integers, which of the following best characterizes the following two statements : A) there exists x such that Q(x) is true B) for every x, -Q(x) is true Only A is true Only B is true Both A and B are true Both A and B are false
If Q(x) is the statement x + 1 > 2x, and the domain is the set of positive integers, which of the following best characterizes the following two statements : A) there exists x such that Q(x) is true B) for every x, -Q(x) is true Only A is true Only B is true Both A and B are true Both A and B are false
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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![### Logic and Set Theory: Analyzing Statements
**Problem Statement:**
Given that \( Q(x) \) is the statement \( x + 1 > 2x \), and the domain is the set of positive integers, which of the following best characterizes the two statements below?
A) There exists \( x \) such that \( Q(x) \) is true.
B) For every \( x \), \( \neg Q(x) \) is true.
**Options:**
1. Only A is true.
2. Only B is true.
3. Both A and B are true.
4. Both A and B are false.
**Analysis:**
Firstly, we analyze the given statement \( Q(x) \):
\[
Q(x): x + 1 > 2x
\]
Simplifying \( Q(x) \):
\[
x + 1 > 2x \implies 1 > x
\]
Since \( x \) is a positive integer (from the domain definition), \( x \) must be greater than or equal to 1. Therefore, the inequality \( 1 > x \) is false for all positive integers \( x \).
**Investigating Statement A:**
Statement A posits that there exists an \( x \) such that \( Q(x) \) is true:
\[
\exists x (x + 1 > 2x)
\]
Because \( Q(x) \) simplifies to \( 1 > x \), and there is no positive integer \( x \) for which this is true, Statement A is false.
**Investigating Statement B:**
Statement B posits that for every \( x \), the negation of \( Q(x) \) is true:
\[
\forall x (\neg Q(x))
\]
Since \( Q(x) \) is equivalent to \( 1 > x \), its negation is:
\[
\neg Q(x): x \geq 1
\]
This inequality \( x \geq 1 \) is true for all positive integers \( x \), hence Statement B is true.
**Conclusion:**
From the analysis, we can conclude that "Only B is true."
Thus, the correct option is:
\[
\boxed{\text{Only B is true.}}
\]](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F86dba1a0-d9e4-4794-91a7-60a099c39063%2F2e401238-c398-4975-b6ef-84490ea530db%2Fwdo39vvl_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Logic and Set Theory: Analyzing Statements
**Problem Statement:**
Given that \( Q(x) \) is the statement \( x + 1 > 2x \), and the domain is the set of positive integers, which of the following best characterizes the two statements below?
A) There exists \( x \) such that \( Q(x) \) is true.
B) For every \( x \), \( \neg Q(x) \) is true.
**Options:**
1. Only A is true.
2. Only B is true.
3. Both A and B are true.
4. Both A and B are false.
**Analysis:**
Firstly, we analyze the given statement \( Q(x) \):
\[
Q(x): x + 1 > 2x
\]
Simplifying \( Q(x) \):
\[
x + 1 > 2x \implies 1 > x
\]
Since \( x \) is a positive integer (from the domain definition), \( x \) must be greater than or equal to 1. Therefore, the inequality \( 1 > x \) is false for all positive integers \( x \).
**Investigating Statement A:**
Statement A posits that there exists an \( x \) such that \( Q(x) \) is true:
\[
\exists x (x + 1 > 2x)
\]
Because \( Q(x) \) simplifies to \( 1 > x \), and there is no positive integer \( x \) for which this is true, Statement A is false.
**Investigating Statement B:**
Statement B posits that for every \( x \), the negation of \( Q(x) \) is true:
\[
\forall x (\neg Q(x))
\]
Since \( Q(x) \) is equivalent to \( 1 > x \), its negation is:
\[
\neg Q(x): x \geq 1
\]
This inequality \( x \geq 1 \) is true for all positive integers \( x \), hence Statement B is true.
**Conclusion:**
From the analysis, we can conclude that "Only B is true."
Thus, the correct option is:
\[
\boxed{\text{Only B is true.}}
\]
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