Determine the sum of the following series. 71=1 (4)n-1 6n

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Author:James Stewart
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Chapter1: Functions And Models
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**Determine the sum of the following series:**

\[ \sum_{n=1}^{\infty} \frac{(4)^{n-1}}{6^n} \]

This is an infinite series where each term is given by the formula \(\frac{(4)^{n-1}}{6^n}\), with \(n\) starting from 1 and going to infinity. The expression involves exponential terms in both the numerator and the denominator.

### Explanation:

The series can be thought of as a geometric series. A geometric series is a series of the form \(\sum_{n=0}^{\infty} ar^n\), where:

- \(a\) is the first term.
- \(r\) is the common ratio between the terms, such that \(0 < |r| < 1\).

In this case, the series starts at \(n=1\), so we can adjust the formula to fit the standard format. Here, the first term \(a\) is \((4)^0 / 6^1\), and the common ratio \(r\) is \(\frac{4}{6} = \frac{2}{3}\).

### Steps to Find the Sum:

1. **Identify the First Term (\(a\)):**
   \[
   a = \frac{(4)^0}{6^1} = \frac{1}{6}
   \]

2. **Identify the Common Ratio (\(r\)):**
   \[
   r = \frac{4}{6} = \frac{2}{3}
   \]

3. **Use the Sum Formula for an Infinite Geometric Series:**
   If \(|r| < 1\), the sum \(S\) of the series is given by:
   \[
   S = \frac{a}{1 - r}
   \]

4. **Calculate the Sum:**
   \[
   S = \frac{\frac{1}{6}}{1 - \frac{2}{3}} = \frac{\frac{1}{6}}{\frac{1}{3}} = \frac{1}{6} \times \frac{3}{1} = \frac{1}{2}
   \]

Thus, the sum of the series is \(\frac{1}{2}\).
Transcribed Image Text:**Determine the sum of the following series:** \[ \sum_{n=1}^{\infty} \frac{(4)^{n-1}}{6^n} \] This is an infinite series where each term is given by the formula \(\frac{(4)^{n-1}}{6^n}\), with \(n\) starting from 1 and going to infinity. The expression involves exponential terms in both the numerator and the denominator. ### Explanation: The series can be thought of as a geometric series. A geometric series is a series of the form \(\sum_{n=0}^{\infty} ar^n\), where: - \(a\) is the first term. - \(r\) is the common ratio between the terms, such that \(0 < |r| < 1\). In this case, the series starts at \(n=1\), so we can adjust the formula to fit the standard format. Here, the first term \(a\) is \((4)^0 / 6^1\), and the common ratio \(r\) is \(\frac{4}{6} = \frac{2}{3}\). ### Steps to Find the Sum: 1. **Identify the First Term (\(a\)):** \[ a = \frac{(4)^0}{6^1} = \frac{1}{6} \] 2. **Identify the Common Ratio (\(r\)):** \[ r = \frac{4}{6} = \frac{2}{3} \] 3. **Use the Sum Formula for an Infinite Geometric Series:** If \(|r| < 1\), the sum \(S\) of the series is given by: \[ S = \frac{a}{1 - r} \] 4. **Calculate the Sum:** \[ S = \frac{\frac{1}{6}}{1 - \frac{2}{3}} = \frac{\frac{1}{6}}{\frac{1}{3}} = \frac{1}{6} \times \frac{3}{1} = \frac{1}{2} \] Thus, the sum of the series is \(\frac{1}{2}\).
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