Answer
$S_{5}=-25$
Work Step by Step
$a_1=-1$ and $a_n=a_5=-9$
$S_n=\frac{n}{2}(a_1+a_n)$
$S_{5}=\frac{5}{2}[-1+(-9)]=\frac{5}{2}(-10)=\frac{-50}{2}=-25$
Algebra and Trigonometry 10th Edition
by Larson, Ron
Published by
Cengage Learning
ISBN 10:
9781337271172
ISBN 13:
978-1-33727-117-2
Chapter 11 - 11.2 - Arithmetic Sequences and Partial Sums - 11.2 Exercises - Page 786: 47
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