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 54: 23

Answer

a) $\exists x P(x)$ $\exists x (P(x) \land A(x))$ b)$\forall x Q(x)$ $\forall x (A(x) \rightarrow Q(x))$ c) $\exists x(\neg R(x))$ $\exists x (A(x) \land \neg R(x))$ d) $\exists x (S(x))$ $\exists x (A(x) \land S(x))$ e) $\neg ( \exists x T(x))$ $\neg ( \exists x (T(x)\land A(x)))$

Work Step by Step

a) There exists a person in your class that can speak hindi. $$\exists x P(x)$$ Let P(x) be "x speaks hindi" and A(x) be " x is in your class". $$\exists x (P(x) \land A(x))$$ b) Everyone means $\forall x$ and if x is in your class then x has to be friendly. $$\forall x Q(x)$$ Let Q(x) be "x is friendly" and A(x) is " x is in your class". $$\forall x (A(x) \rightarrow Q(x))$$ c) There is a person means $\exists x$ and x has to be in your class and cannot be born in california. $$\exists x(\neg R(x))$$ Let R(x) be "x is born in california" and A(x) be "x is in your class". $$\exists x (A(x) \land \neg R(x))$$ d) There is a student means $\exists x$ and x has to be in your class and has to have been in a movie. $$\exists x (S(x))$$ Let S(x) be "x has been in a movie" and A(x) be "x is in your class". $$\exists x (A(x) \land S(x))$$ e) No student means $\neg (\exists x)$ and x has to be in your class and has to have taken a course in logic programming. $$\neg ( \exists x T(x))$$ Let T(x) be "x has taken a course in logic programming" and A(x) be " x is in your class". $$\neg ( \exists x (T(x)\land A(x)))$$
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