Algebra and Trigonometry 10th Edition

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: 46

Answer

$S_{7}=70$

Work Step by Step

$a_1=1$ and $a_n=a_7=19$ $S_n=\frac{n}{2}(a_1+a_n)$ $S_{7}=\frac{7}{2}(1+19)=\frac{7}{2}(20)=\frac{140}{2}=70$
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