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 1.3 - Propositional Equivalences - Exercises - Page 35: 33

Answer

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Work Step by Step

To show that these are not logically equivalent, we need only find one assignment of truth values to p, q, r, and s for which the truth values of (p _, q) _, (r _, s) and (p _, r) _, (q _, s) differ . Let us try to make the first one false. That means we have to make r _, s false, so we want r to be true and s to be false. If we let p and q be false, then each of the other three simple conditional statements (p _, q, p _, r, and q _, s) will be true. Then (p-t q) _, (r _, s) will be T-t F, which is false; but (p-t r) _, (q _, s) will be T-t T, which is true.
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