Precalculus: Mathematics for Calculus, 7th Edition

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

Chapter 12 - Review - Exercises - Page 891: 58

Answer

converges, $\quad $sum = $\displaystyle \frac{1}{2}(3+\sqrt{3})$

Work Step by Step

An infinite geometric series is a series of the form $ a+ar+ar^{2}+ar^{3}+\cdots+ar^{n-1}+\cdots$ An infinite geometric series for which $|r| < 1$ has the sum $S=\displaystyle \frac{a}{1-r}$ If $|r| \geq 1$, the series diverges (the sum does not exist). ------------ $a=1$ $ r=\displaystyle \frac{3^{-1/2}}{1}=3^{-1/2}=\frac{1}{\sqrt{3}}\approx 0.5774, \quad$ $ |r| < 1, $so the series is convergent, $S=\displaystyle \frac{1}{1-\frac{1}{\sqrt{3}}}= \frac{1}{\frac{\sqrt{3}-1}{\sqrt{3}}}=\frac{\sqrt{3}}{\sqrt{3}-1}$ $=\displaystyle \frac{\sqrt{3}}{\sqrt{3}-1}\times\frac{\sqrt{3}+1}{\sqrt{3}+1}=\frac{3+\sqrt{3}}{3-1}$ $=\displaystyle \frac{1}{2}(3+\sqrt{3})$
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