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 3.2 - Page 117: 26

Answer

Converse: $\forall$ real numbers x, if x>0, then $x^2 \geq 1.$ Inverse: $\forall$ real numbers x, if $x^2 < 1$, then x $\leq$ 0. Contrapositive: $\forall$ real numbers x, if x $\leq$ 0, then $x^2 < 1$. All statements are false. Counterexamples: Contrapositive: Let x=-2, then $x^2 = 4$ which is not less than 1. (since the contrapositive is logically equivalent to the original statement, the original statement is also false) Inverse: Let x= 1/2. Then $x^2 = 1/4 < 1$, but x is not less than or equal to 0. Converse: Let x= 1/2. Then x>0, but $x^2 =1/4$ is not greater than or equal to 1.

Work Step by Step

A statement of the form: $\forall x \in D$, if P(x) then Q(x), has as its contrapositive statement: $\forall x \in D$, if ~Q(x) then ~P(x), as its converse statement: $\forall x \in D$, if Q(x) then P(x), and as its inverse statement: $\forall x \in D$, if ~P(x) then ~Q(x).
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