Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 1 - Section 1.4 - Predicates and Quantifiers - Exercises - Page 53: 18

Answer

a) $ P(-2) \lor P(-1) \lor P(0) \lor P(1) \lor P(2)$ b) $ P(-2) \land P(-1) \land P(0) \land P(1) \land P(2)$ c) $ \neg P(-2) \lor \neg P(-1) \lor \neg P(0) \lor \neg P(1) \lor \neg P(2)$ d) $ \neg P(-2) \land \neg P(-1) \land \neg P(0) \land \neg P(1) \land \neg P(2)$ e) $ \neg (P(-2) \lor P(-1) \lor P(0) \lor P(1) \lor P(2))$ f) $\neg ( P(-2) \land P(-1) \land P(0) \land P(1) \land P(2))$

Work Step by Step

INTERPRETATION SYMBOLS Negation : $\neg p$ Disjunction : $p \lor q$ Conjunction : $ p \land q$ Existential quantification : $\exists$ $ x$ $P(x)$ Universal quantification : $\forall$ $x$ $P(x)$ Solution- a) $\exists$ $ x$ $P(x)$ means that there exists a value of x for which P(x) is true, thus P(-2) is true or P(-1) is true or P(0) is true or P(1) is true or P(2) is true. So, we can rewrite the proposition as: $$ P(-2) \lor P(-1) \lor P(0) \lor P(1) \lor P(2)$$ b) $\forall$ $ x$ $P(x)$ means that there exists a value of x for which P(x) is true, thus P(-2) is true and P(-1) is true and P(0) is true and P(1) is true and P(2) is true. So, we can rewrite the proposition as: $$ P(-2) \land P(-1) \land P(0) \land P(1) \land P(2)$$ c)$\exists$ $ x$ $\neg P(x)$ means that there exists a value of x for which $\neg P(x)$ is true, thus $\neg P(-2)$ is true or $\neg P(-1)$ is true or $\neg P(0)$ is true or $\neg P(1)$ is true or $\neg P(2)$ is true. So, we can rewrite the proposition as: $$ \neg P(-2) \lor \neg P(-1) \lor \neg P(0) \lor \neg P(1) \lor \neg P(2)$$ d)$\forall$ $ x$ $\neg P(x)$ means that there exists a value of x for which P(x) is true, thus $\neg P(-2)$ is true and $\neg P(-1)$ is true and $\neg P(0)$ is true and $\neg P(1)$ is true and $\neg P(2)$ is true. So, we can rewrite the proposition as: $$ \neg P(-2) \land \neg P(-1) \land \neg P(0) \land \neg P(1) \land \neg P(2)$$ e) $\neg$ $ \exists x$ $P(x)$ is the negation of $ \exists x$ $P(x)$ in part a) , thus we take the negation of part (a): $$ \neg (P(-2) \lor P(-1) \lor P(0) \lor P(1) \lor P(2))$$ f) $\neg \forall x$ $P(x)$ is the negation of $\forall$$ x$ $P(x)$ in part b) , thus we take the negation of the result in part b): $$\neg ( P(-2) \land P(-1) \land P(0) \land P(1) \land P(2))$$
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