Math Problem Statement

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For the series below, calculate the number of terms n that must be added in order to find the sum to the indicated accuracy. \( \sum_{n=1}^{\infty} \frac{(-1)^n 300}{n^{0.6}} \), with error \( | \text{error} | < 5 \).

Solution

The problem asks to determine the number of terms nn that must be added in the series to achieve an error less than 5.

Series Expression:

n=1(1)n300n0.6\sum_{n=1}^{\infty} \frac{(-1)^n 300}{n^{0.6}} where the error condition is error<5|\text{error}| < 5.

Step-by-Step Approach:

  1. Understanding the Series: This is an alternating series, and its general term is: an=(1)n300n0.6a_n = \frac{(-1)^n 300}{n^{0.6}} For alternating series, the error after adding nn terms is approximately the absolute value of the first omitted term.

  2. Error Condition: The first omitted term (the next term after the nn-th term) is: an+1=300(n+1)0.6a_{n+1} = \frac{300}{(n+1)^{0.6}} The error condition requires: 300(n+1)0.6<5\left| \frac{300}{(n+1)^{0.6}} \right| < 5

  3. Solve for nn: Solving the inequality for nn, 300(n+1)0.6<5\frac{300}{(n+1)^{0.6}} < 5 Simplifying this, (n+1)0.6>3005=60(n+1)^{0.6} > \frac{300}{5} = 60 Raising both sides to the power of 10.6\frac{1}{0.6}, n+1>6010.6=6053132.6n+1 > 60^{\frac{1}{0.6}} = 60^{\frac{5}{3}} \approx 132.6 Therefore, n>131.6n > 131.6 So the smallest integer nn that satisfies this condition is n=132n = 132.

Conclusion:

To ensure that the error is less than 5, you must sum at least 132 terms of the series. Therefore, n=35n = 35 in the image is too small.

Would you like more details on any of the steps?


Here are 5 related questions you might find interesting:

  1. How do you estimate the error in an alternating series?
  2. How does the alternating series test guarantee convergence?
  3. What would the error be if you summed only 35 terms?
  4. How would this change if the exponent in the denominator was different?
  5. What if the numerator's constant was different?

Tip: Always remember that for alternating series, the error is typically dominated by the first omitted term after partial sums.

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Math Problem Analysis

Mathematical Concepts

Alternating Series
Error Bound
Convergence

Formulas

Error approximation: |a_{n+1}| < error threshold

Theorems

Alternating Series Estimation Theorem

Suitable Grade Level

Grades 11-12 (Advanced High School)