Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 10: Infinite Sequences and Series - Section 10.1 - Sequences - Exercises 10.1 - Page 569: 22

Answer

$a_{n}=2(2n-1), \quad n=1,2,3...$

Work Step by Step

The differences between terms are 2,2,2,2,... These are constant, similar to the sequence of natural numbers: 1,2,3,4,... where the difference between terms is $1$. If we multiply each term of (1,2,3,4,...) with 2, we get $2,4,6,8,10,...$ The difference between terms is now $2$, as in the problem. We find a relationship between this sequence and the one given by the problem by observing the pattern: $ 2=2+0\quad$ = $2n+2(n-1)=4n-2$ when n=$1,$ $ 6=4+2\quad$ = $2n+2(n-1)=4n-2$ when n=$2,$ $ 10=6+4\quad$ = $2n+2(n-1)=4n-2$ when n=$3,$ $ 14=8+6\quad$ = $2n+2(n-1)=4n-2$ when n=$4$ $ 18=10+8\quad$ = $2n+2(n-1)=4n-2$ when n=$5$ $...$ $a_{n}=4n-2=2(2n-1), \quad n=1,2,3...$ $a_{n}=2(2n-1), \quad n=1,2,3...$
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