Math Problem Statement

Evaluate the convergence of the infinite series involving trigonometric and polynomial terms: ∑ (sin²(2ⁿ) / n⁴) from n=1 to ∞.

Solution

The given image shows the infinite series:

n=1sin2(2n)n4\sum_{n=1}^{\infty} \frac{\sin^2(2^n)}{n^4}

This series involves a combination of trigonometric functions and powers of nn. To analyze this, let's break it down:

1. Behavior of the Numerator:

The term sin2(2n)\sin^2(2^n) is bounded between 0 and 1 because for any real number xx, sin2(x)\sin^2(x) takes values in the range [0,1][0, 1]. Hence, the numerator does not grow significantly as nn increases.

2. Denominator Growth:

The term n4n^4 grows very rapidly as nn increases. The factor n4n^4 in the denominator suggests that the terms of the series decay quickly, meaning the series has a good chance of converging.

3. Comparison Test for Convergence:

We can use a comparison test with a simpler series. Consider the series:

n=11n4\sum_{n=1}^{\infty} \frac{1}{n^4}

This is a p-series with p=4p = 4, and it is known to converge since p>1p > 1. Because sin2(2n)\sin^2(2^n) is bounded between 0 and 1, we have:

0sin2(2n)n41n40 \leq \frac{\sin^2(2^n)}{n^4} \leq \frac{1}{n^4}

Thus, by the comparison test, since n=11n4\sum_{n=1}^{\infty} \frac{1}{n^4} converges, the original series also converges.

Conclusion:

The series n=1sin2(2n)n4\sum_{n=1}^{\infty} \frac{\sin^2(2^n)}{n^4} converges.

Would you like more details on how to compute the exact sum, or any specific aspects of this problem?

Here are some questions you might explore further:

  1. How does the rapid growth of n4n^4 ensure convergence in series?
  2. Can we approximate the sum of the series numerically?
  3. What if the power in the denominator was n2n^2 instead of n4n^4?
  4. How do different types of tests help in determining convergence of series?
  5. What are other examples of convergent series involving trigonometric functions?

Tip: When testing for convergence, comparison tests are very useful when you can bound the terms of your series with a simpler, known series.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Series Convergence
Trigonometric Functions
Comparison Test

Formulas

sin²(x) for real x
p-series: ∑ 1/n^p converges if p > 1
Comparison Test

Theorems

Comparison Test
p-Series Convergence Theorem

Suitable Grade Level

Undergraduate Level