Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 12 - Section 12.3 - Geometric Sequences - 12.3 Exercises - Page 865: 63

Answer

$\displaystyle \frac{211}{27}$

Work Step by Step

See p. 861. For the geometric sequence $a_{n}=ar^{n-1}$ the nth partial sum$ S_{n}=\displaystyle \sum_{k=1}^{n}ar^{k-1}$ (where $r\neq 1$) is given by$ \displaystyle \quad S_{n}=a\cdot\frac{1-r^{n}}{1-r}$ --------------- $S_{n}=3\displaystyle \times\cdot\frac{1-(\frac{2}{3})^{5}}{1-(\frac{2}{3})}=3\times\frac{3^{5}-2^{5}}{3^{5}}\div\frac{1}{3}$ $= 3\displaystyle \times\frac{211}{3^{5}}\times 3$ $=\displaystyle \frac{211}{27}$
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