Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 3 - The Logic of Quantified Statements - Exercise Set 3.3 - Page 130: 30

Answer

a. Version with interchanged quantifiers: $\forall x \in \mathbb{R}$, $\exists y \in \mathbb{R}^{-}$ such that x > y. b. Both the original and the interchanged statement are true.

Work Step by Step

b. The original statement says there is a real number that is greater than every negative real number. This is true. Let that real number x be 0 which is greater than every negative real number. The statement with interchanged quantifiers says for every real number x, there is a negative real number y that is less than x. This is true. Let y = -|x| - 1. Then x>y for all x.
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