Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 2 - Section 2.4 - Sequences and Summations - Exercises - Page 168: 12

Answer

All four sequences check the recurrence relation

Work Step by Step

We are given the recurrence relation: $$\begin{align}a_n=-3a_{n-1}+4a_{n-2}.\end{align}\tag 1$$ We will check if the given sequences check that recurrence relation. a) We substitute $a_{n-1}=0$ and $a_{n-2}=0$ in Eq. $(1)$ and we get: $$-3(0)+4(0)=0\checkmark.$$ b) We substitute $a_{n-1}=1$ and $a_{n-2}=1$ in Eq. $(1)$ and we get: $$-3(1)+4(1)=1\checkmark.$$ c) We substitute $a_{n-1}=(-4)^{n-1}$ and $a_{n-2}=(-4)^{n-2}$ in Eq. $(1)$ and we get: $$\begin{align*} -3(-4)^{n-1}+4(-4)^{n-2}&=-3(-4)^{n-1}-(-4)^{n-1}\\ &=-4(-4)^{n-1}\\ &=(-4)^n\checkmark. \end{align*}$$ d) We substitute $a_{n-1}=2(-4)^{n-1}+3$ and $a_{n-2}=2(-4)^{n-2}+3$ in Eq. $(1)$ and we get: $$\begin{align*} -3[2(-4)^{n-1}+3]+4[2(-4)^{n-2}+3]&=-6(-4)^{n-1}-9+8(-4)^{n-2}+12\\ &=-6(-4)^{n-1}-2(-4)^{n-2}+3\\ &=-8(-4)^{n-1}+3\\ &=2(-4)^n+3\checkmark. \end{align*}$$
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