Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 10 - Section 10.2 - Arithmetic Sequences - Exercise Set - Page 1059: 35



Work Step by Step

Formula to calculate the sum of an arithmetic sequence is: $S_n=\dfrac{n}{2}(a_1+a_n)$ ...(1) Here, $a_1: $ First term and $d=$ common difference Since, we have $d=a_2-a_1=10-4=6$ and $a_{20}=4+6(20-1)=118$ Then, our first (1) equation becomes: $S_n=\dfrac{20}{2}(4+118)=10(122)=1220$
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