Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 11 - Review Exercises - Page 841: 56

Answer

$S_{4}=720$

Work Step by Step

$\displaystyle \sum_{i=1}^{4}6(3)^{i}=6(3)^{1}+6(3)^{2}+6(3)^{3}+6(3)^{4}$ $a_1=6(3)^1=18$ $r=\frac{a_2}{a_1}=\frac{6(3)^2}{6(3)^1}=3$ $S_{4}=a_1(\frac{1-r^n}{1-r})=18(\frac{1-3^4}{1-3})=18\frac{-80}{-2}=720$
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