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: 23

Answer

\[ T(2)=1,\quad T(3)=1,\quad T(4)=1,\quad T(5)=1,\quad T(6)=1,\quad T(7)=1. \] All paths eventually reach \(T(1)=1\). This is, of course, the classic Collatz‐type behavior—though whether *all* integers ultimately reach 1 is the famous open “3n+1 problem.”

Work Step by Step

First, recall the given definition (which resembles the Collatz or “3n+1” iteration), for integers \(n \ge 1\): \[ T(n) \;=\; \begin{cases} 1, & \text{if }n=1,\\[6pt] T\!\bigl(\tfrac{n}{2}\bigr), & \text{if }n\text{ is even},\\[6pt] T\!\bigl(3n+1\bigr), & \text{if }n\text{ is odd and }n>1. \end{cases} \] We want to compute \(T(2), T(3), T(4), T(5), T(6), T(7)\). All of these eventually reduce to \(T(1)\), which is given as \(1\). Here are the step‐by‐step chains: --- ### 1. \(T(2)\) - \(2\) is even, so \(T(2) = T(2/2) = T(1)\). - \(T(1) = 1\) by definition. Hence \(\boxed{T(2)=1}.\) --- ### 2. \(T(3)\) \(3\) is odd (\(\neq 1\)), so \(T(3) = T(3\cdot3 + 1) = T(10)\). \(10\) is even, so \(T(10) = T(10/2) = T(5)\). \(5\) is odd (\(\neq 1\)), so \(T(5) = T(3\cdot5 + 1) = T(16)\). \(16\) is even, so \(T(16) = T(16/2) = T(8)\). \(8\) is even, so \(T(8) = T(8/2) = T(4)\). \(4\) is even, so \(T(4) = T(4/2) = T(2)\). We already found \(T(2)=1\). So the chain \(3 \to 10 \to 5 \to 16 \to 8 \to 4 \to 2 \to 1\) leads to \(T(3)=1\). Hence \(\boxed{T(3)=1}.\) --- ### 3. \(T(4)\) - \(4\) is even, so \(T(4) = T(4/2) = T(2)\). - From above, \(T(2)=1\). Thus \(\boxed{T(4)=1}.\) --- ### 4. \(T(5)\) \(5\) is odd, so \(T(5) = T(3\cdot5 + 1) = T(16)\). \(16\) is even \(\to T(16)=T(8)\). \(8\) is even \(\to T(8)=T(4)\). \(4\) is even \(\to T(4)=T(2)\). \(T(2)=1\). Hence \(\boxed{T(5)=1}.\) *(We already saw most of this chain when doing \(T(3)\).)* --- ### 5. \(T(6)\) \(6\) is even, so \(T(6) = T(6/2) = T(3)\). From above, \(T(3)=1\). So \(\boxed{T(6)=1}.\) --- ### 6. \(T(7)\) \(7\) is odd, so \(T(7) = T(3\cdot7 + 1) = T(22)\). \(22\) is even \(\to T(22)=T(11)\). \(11\) is odd \(\to T(11)=T(34)\). \(34\) is even \(\to T(34)=T(17)\). \(17\) is odd \(\to T(17)=T(52)\). \(52\) is even \(\to T(52)=T(26)\). \(26\) is even \(\to T(26)=T(13)\). \(13\) is odd \(\to T(13)=T(40)\). \(40\) is even \(\to T(40)=T(20)\). \(20\) is even \(\to T(20)=T(10)\). \(10\) is even \(\to T(10)=T(5)\). \(5\) is odd \(\to T(5)=T(16)\). \(16\) is even \(\to T(16)=T(8)\). \(8\) is even \(\to T(8)=T(4)\). \(4\) is even \(\to T(4)=T(2)\). \(T(2)=1\). Thus \(\boxed{T(7)=1}.\)
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