Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 11 - Section 11.2 - Series - 11.2 Exercises - Page 716: 32

Answer

$\frac{7}{3}$

Work Step by Step

We can split the initial series into the sum of two separate geometric series and evaluate their sums separately: $\sum^{\infty}_{n=1} (-0.2)^n$ + $\sum^{\infty}_{n=1} (0.6)^{n-1}$ We can see that $\sum^{\infty}_{n=1} (-0.2)^n$ is a geometric series, with initial term $ a = 0.2$ and $r = -0.2$ We use the geometric series formula $$\sum^{\infty}_{n=0} ar^n = \frac{a}{1-r}$$ which gives us $\frac{-0.2}{1-(-0.2)} = \frac{-0.2}{1.2}$ Likewise, we can see that $\sum^{\infty}_{n=1} (0.6)^{n-1}$ is a geometric series, with initial term $ a = 1$ and $r = 0.6$ Using the same formula, we get $\frac{1}{1-0.6} = \frac{1}{0.4}$ We now add $ \frac{-0.2}{1.2}$ and $\frac{1}{0.4}$ together and get $\frac{-0.2 + 3}{1.2} = \frac{2.8}{1.2} = \frac{7}{3} $
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