,(-1)" converges conditionally, but not absolutely. Show all work. 3n Prove E
Advanced Engineering Mathematics
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Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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![**Homework Problem on Series Convergence**
**Problem**
**a.** Prove \( \sum_{n=1}^{\infty} \frac{(-1)^n}{3n} \) converges conditionally, but not absolutely. Show all work.
**b.** What value of \( n \) must you use to compute the \(n^{th}\) partial sum, \( S_n \), so that \( S_n \) is accurate to within 0.005? You do NOT need to calculate \( S_n \); just tell me what \( n \) works. Show all work.
**Solution Steps**
### Part a: Conditional Convergence Proof
1. **Test for Absolute Convergence:**
Consider the absolute value of the terms of the series:
\[
\sum_{n=1}^{\infty} \left| \frac{(-1)^n}{3n} \right| = \sum_{n=1}^{\infty} \frac{1}{3n}
\]
This is a constant multiple of the harmonic series:
\[
\sum_{n=1}^{\infty} \frac{1}{n}
\]
Since the harmonic series diverges, \(\sum_{n=1}^{\infty} \frac{1}{3n} \) also diverges. Therefore, the series does not converge absolutely.
2. **Test for Conditional Convergence:**
Use the Alternating Series Test (Leibniz's Test) for the series \( \sum_{n=1}^{\infty} \frac{(-1)^n}{3n} \).
The Alternating Series Test requires checking two conditions:
- The terms \( a_n = \frac{1}{3n} \) decrease monotonically.
- \(\lim_{n \to \infty} a_n = 0 \)
Both conditions are satisfied:
- \( a_{n+1} = \frac{1}{3(n+1)} < \frac{1}{3n} = a_n \) for all \( n \), so the terms decrease monotonically.
- \(\lim_{n \to \infty} \frac{1}{3n} = 0\)
Thus, by the Alternating Series Test, the series \( \sum_{n=1](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F32c25cea-359b-456d-b95a-7b7f50563263%2Fa5e17913-80c7-4273-920d-073205153ddd%2Feg40gp3.png&w=3840&q=75)
Transcribed Image Text:**Homework Problem on Series Convergence**
**Problem**
**a.** Prove \( \sum_{n=1}^{\infty} \frac{(-1)^n}{3n} \) converges conditionally, but not absolutely. Show all work.
**b.** What value of \( n \) must you use to compute the \(n^{th}\) partial sum, \( S_n \), so that \( S_n \) is accurate to within 0.005? You do NOT need to calculate \( S_n \); just tell me what \( n \) works. Show all work.
**Solution Steps**
### Part a: Conditional Convergence Proof
1. **Test for Absolute Convergence:**
Consider the absolute value of the terms of the series:
\[
\sum_{n=1}^{\infty} \left| \frac{(-1)^n}{3n} \right| = \sum_{n=1}^{\infty} \frac{1}{3n}
\]
This is a constant multiple of the harmonic series:
\[
\sum_{n=1}^{\infty} \frac{1}{n}
\]
Since the harmonic series diverges, \(\sum_{n=1}^{\infty} \frac{1}{3n} \) also diverges. Therefore, the series does not converge absolutely.
2. **Test for Conditional Convergence:**
Use the Alternating Series Test (Leibniz's Test) for the series \( \sum_{n=1}^{\infty} \frac{(-1)^n}{3n} \).
The Alternating Series Test requires checking two conditions:
- The terms \( a_n = \frac{1}{3n} \) decrease monotonically.
- \(\lim_{n \to \infty} a_n = 0 \)
Both conditions are satisfied:
- \( a_{n+1} = \frac{1}{3(n+1)} < \frac{1}{3n} = a_n \) for all \( n \), so the terms decrease monotonically.
- \(\lim_{n \to \infty} \frac{1}{3n} = 0\)
Thus, by the Alternating Series Test, the series \( \sum_{n=1
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