# Chapter 12 - Sequences and Series - Chapter Review - Review Exercises - Page 662: 33

$$\frac{{27}}{5}$$

#### Work Step by Step

\eqalign{ & 9 - 6 + 4 - \frac{8}{3} + \cdots \cr & {\text{Sum of a Geometric Series }}\left( {{\text{see page 635}}} \right) \cr & {\text{The infinite geometric series}} \cr & a + ar + a{r^2} + a{r^3} + \cdots \cr & {\text{converges}}{\text{, if }}r{\text{ is in }}\left( { - 1,1} \right),{\text{ to the sum }}\frac{a}{{1 - r}}.{\text{ And diverges if }}r{\text{ is not in }}\left( { - 1,1} \right) \cr & {\text{then this is a geometric series}}{\text{, with }}a = {a_1} = 9 \cr & r = \frac{{ - 6}}{9} = - \frac{2}{3} \cr & {\text{Since }}r{\text{ is in the interval }}\left( { - 1,1} \right),{\text{ the series converges and has a sum }}\frac{a}{{1 - r}} \cr & \frac{a}{{1 - r}} = \frac{9}{{1 - \left( { - 2/3} \right)}} \cr & {\text{simplifying}} \cr & \frac{a}{{1 - r}} = \frac{9}{{5/3}} \cr & \frac{a}{{1 - r}} = \frac{{27}}{5} \cr}

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