College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 9 - Section 9.2 - Arithmetic Sequences - 9.2 Assess Your Understanding - Page 654: 52

Answer

$-7920$

Work Step by Step

There are $90$ terms, and they form an arithmetic sequence with $d=a_{n+1}-a_{n}=3-2(n+1)-(3-2n)$ $=3-2n-2-3+2n$ $=-2$ $a_{1}=3-2(1)=1,$ $a_{90}=3-2(90)=-177$ Sum of the First $n$ Terms of an arithmetic sequence: $S_{n}=\displaystyle \frac{n}{2}\left(a_{1}+a_{n}\right)$ $S_{90}=\displaystyle \frac{90}{2}(1+(-177))=45(-176)=-7920$
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