Find the interval of convergence of (x - 9)" In (9n) n=2

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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### Interval of Convergence

To determine the interval of convergence for the given series:

\[ \sum_{n=2}^{\infty} \frac{(x - 9)^n}{\ln(9n)} \]

we must analyze the series and apply convergence tests such as the Ratio Test or the Root Test.

#### Steps to Solve:

1. **Define the General Term of the Series:** Identify the general term \( a_n \) from the series:
   \[
   a_n = \frac{(x - 9)^n}{\ln(9n)}
   \]

2. **Apply the Ratio Test:** The Ratio Test is often used to determine the radius of convergence for power series. According to the Ratio Test, compute:
   \[
   L = \lim_{n \to \infty} \left| \frac{a_{n+1}}{a_n} \right|
   \]

   Here,
   \[
   a_{n+1} = \frac{(x - 9)^{n+1}}{\ln[9(n + 1)]} 
   \]

   Therefore,
   \[
   \left| \frac{a_{n+1}}{a_n} \right| = \left| \frac{(x - 9)^{n+1}}{\ln[9(n + 1)]} \times \frac{\ln(9n)}{(x - 9)^n} \right| = \left| (x - 9) \frac{\ln(9n)}{\ln[9(n + 1)]} \right|
   \]

3. **Simplify and Find the Limit:** Simplify the expression within the limit and evaluate as \( n \) approaches infinity:
   \[
   L = \lim_{n \to \infty} \left| (x - 9) \frac{\ln(9n)}{\ln[9(n + 1)]} \right|
   \]

   Notice that as \( n \to \infty \), \( \ln[9(n + 1)] \) behaves similarly to \( \ln(9n) \). Thus, the fraction approaches 1, yielding:
   \[
   L = |x - 9|
   \]

4. **Determine the Radius of Convergence:** According to the Ratio Test, the
Transcribed Image Text:### Interval of Convergence To determine the interval of convergence for the given series: \[ \sum_{n=2}^{\infty} \frac{(x - 9)^n}{\ln(9n)} \] we must analyze the series and apply convergence tests such as the Ratio Test or the Root Test. #### Steps to Solve: 1. **Define the General Term of the Series:** Identify the general term \( a_n \) from the series: \[ a_n = \frac{(x - 9)^n}{\ln(9n)} \] 2. **Apply the Ratio Test:** The Ratio Test is often used to determine the radius of convergence for power series. According to the Ratio Test, compute: \[ L = \lim_{n \to \infty} \left| \frac{a_{n+1}}{a_n} \right| \] Here, \[ a_{n+1} = \frac{(x - 9)^{n+1}}{\ln[9(n + 1)]} \] Therefore, \[ \left| \frac{a_{n+1}}{a_n} \right| = \left| \frac{(x - 9)^{n+1}}{\ln[9(n + 1)]} \times \frac{\ln(9n)}{(x - 9)^n} \right| = \left| (x - 9) \frac{\ln(9n)}{\ln[9(n + 1)]} \right| \] 3. **Simplify and Find the Limit:** Simplify the expression within the limit and evaluate as \( n \) approaches infinity: \[ L = \lim_{n \to \infty} \left| (x - 9) \frac{\ln(9n)}{\ln[9(n + 1)]} \right| \] Notice that as \( n \to \infty \), \( \ln[9(n + 1)] \) behaves similarly to \( \ln(9n) \). Thus, the fraction approaches 1, yielding: \[ L = |x - 9| \] 4. **Determine the Radius of Convergence:** According to the Ratio Test, the
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