Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 5 - Sequences, Mathematical Induction, and Recursion - Exercise Set 5.9 - Page 335: 25

Answer

See explanation

Work Step by Step

Below is the core reason why the proposed definition fails to produce a well‐defined function. The “definition” is \[ G(n) \;=\; \begin{cases} 1, & \text{if }n=1,\\[4pt] G\!\bigl(\tfrac{n}{2}\bigr), & \text{if }n\text{ is even},\\[4pt] 2 + G(3n - 5), & \text{if }n\text{ is odd and }n>1. \end{cases} \] We want to see that there is **no** consistent way to assign values to \(G\) for *all* \(n\ge1\). --- ## Key Contradiction at \(n=5\) 1. For \(n=5\) (which is odd and \(>1\)), the rule says: \[ G(5) \;=\; 2 + G\bigl(3\cdot 5 - 5\bigr) \;=\; 2 + G(10). \] 2. But \(10\) is even, so: \[ G(10) \;=\; G\!\bigl(\tfrac{10}{2}\bigr) \;=\; G(5). \] 3. Combining these: \[ G(5) \;=\; 2 + G(10) \;=\; 2 + G(5). \] This implies \(0 = 2\), a direct contradiction. Thus, as soon as we try to define \(G(5)\), we find it depends on \(G(10)\), but \(G(10)\) in turn depends back on \(G(5)\), forcing \(G(5)=2+G(5)\). No single integer value for \(G(5)\) can satisfy that equation. --- ## Conclusion A properly defined function must assign exactly one well‐defined value to each input in its domain. Here, the attempt to define \(G\) leads to a logical impossibility for \(n=5\). Therefore, **the “definition” of \(G\) is not well‐defined**—Student D’s claim is justified.
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