Math Problem Statement

Given the sequence {a_n} = n / (n^2 + 1), what is its behavior for increasing n?

Solution

The given sequence {an}\{a_n\} is defined as:

an=nn2+1a_n = \frac{n}{n^2 + 1}

This represents a sequence where each term is computed based on the index nn, with the general formula involving both nn and its square.

Properties and Analysis:

  1. Limit as nn \to \infty:
    As nn increases, the value of the sequence approaches a limit. We can analyze the limit of ana_n as nn \to \infty: limnnn2+1=limnnn2(1+1n2)=limn1n(1+1n2)=0\lim_{n \to \infty} \frac{n}{n^2 + 1} = \lim_{n \to \infty} \frac{n}{n^2(1 + \frac{1}{n^2})} = \lim_{n \to \infty} \frac{1}{n(1 + \frac{1}{n^2})} = 0 Therefore, the sequence tends towards zero as nn becomes large.

  2. Behavior for small nn:
    For small values of nn, we can calculate specific terms: a1=112+1=12,a2=222+1=25,a3=332+1=310a_1 = \frac{1}{1^2 + 1} = \frac{1}{2}, \quad a_2 = \frac{2}{2^2 + 1} = \frac{2}{5}, \quad a_3 = \frac{3}{3^2 + 1} = \frac{3}{10} So the terms decrease as nn increases.

  3. Monotonicity and boundedness:
    The sequence is decreasing for n1n \geq 1 since an+1<ana_{n+1} < a_n for positive nn, and all terms are positive. It is also bounded below by 0, as seen in the limit behavior.

Would you like further details on these concepts or on how the sequence behaves for larger values of nn?


Here are 5 related questions for deeper exploration:

  1. How do you prove rigorously that the sequence is decreasing?
  2. Can the sequence ana_n be expressed as a sum or product of simpler sequences?
  3. What happens if you modify the denominator, for example n21n^2 - 1?
  4. How would the sequence change if the numerator was a constant instead of nn?
  5. How does the rate of convergence to zero compare with other similar sequences?

Tip: Investigating the derivative of the general term can help confirm whether a sequence is increasing or decreasing.

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Math Problem Analysis

Mathematical Concepts

Sequences
Limits
Monotonicity
Convergence

Formulas

a_n = n / (n^2 + 1)
lim (n -> infinity) n / (n^2 + 1) = 0

Theorems

Limit Theorem
Monotonicity of Sequences

Suitable Grade Level

Grades 11-12 or early university