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 131: 46

Answer

a. True. Both triangles a and c lie above all the squares. b. Formal version: ∃x(Triangle(x) ∧ (∀y(Square(y) → Above(x, y)))) c. Formal negation: ∀x(∼Triangle(x) ∨ (∃y (Square (y)∧ ∼Above(x, y))))

Work Step by Step

Recall the negation of a for all statement: ~($\forall x$ in D, P(x)) $\equiv \exists x$ in D such that ~P(x). Recall the negation of an exists statement: ~($\exists x$ in D, P(x)) $\equiv \forall x$ in D such that ~P(x). To negate a multiply quantified statement, apply the laws in stages moving left to right along the sentence. Negation of $\land$ is $\lor$. Negation of $\lor$ is $\land$.
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