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Q9E
Expert-verifiedDetermine whether the geometric series is convergent or divergent..If it is convergent,find its sum.
\(\sum\limits_{n = 1}^\infty {\frac{{{{( - 3)}^{n - 1}}}}{{{4^n}}}} \)
The given series is Convergent and Sum=\(\frac{1}{7}\)..\(\)
Given Series \(\sum\limits_{n = 1}^\infty {\frac{{{{( - 3)}^{n - 1}}}}{{{4^n}}}} = \frac{1}{4} - \frac{3}{{16}} + \frac{9}{{64}} - \frac{{27}}{{256}} + ......\)
Common Ratio of this series=\(\frac{{{a_{n + 1}}}}{{{a_n}}}\)=\(\frac{{ - 3}}{{16}}*\frac{4}{1} = - \frac{3}{4}\)
Since,\(|r| = \frac{3}{4} < 1\)
Therefore,the series is convergent..
Formula for infinite sum of a gp is =\(\frac{a}{{1 - r}}\)
Where a is first term and r is common ratio.
\({S_\infty } = \frac{{\frac{1}{4}}}{{1 + \frac{3}{4}}} = \frac{1}{7}\)
Hence,The Series is convergent and Sum=\(\frac{8}{3}\)
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