Math Problem Statement

Question 1: Suppose (an) is a sequence defined by an = 1 n+1 for n = 1, 2, 3, . . ..

  1. Prove that the sequence (an) converges.
  2. Find the limit of the sequence as n → ∞.
  3. Explain intuitively why this limit makes sense in terms of the behavior of the sequence’s terms as n increases.

Solution

To address this problem comprehensively, let's tackle each part step by step.

Part 1: Prove that the sequence (an)(a_n) converges

The sequence (an)(a_n) is given by: an=1n+1a_n = \frac{1}{n+1} for n=1,2,3,n = 1, 2, 3, \ldots.

To prove that (an)(a_n) converges, let's analyze its behavior as nn becomes very large.

  1. Monotonicity: Notice that an=1n+1a_n = \frac{1}{n+1} is positive for all n1n \geq 1 and decreases as nn increases. To confirm this, observe that an+1=1n+2a_{n+1} = \frac{1}{n+2}, and since n+2>n+1n+2 > n+1, it follows that 1n+2<1n+1\frac{1}{n+2} < \frac{1}{n+1}. Therefore, (an)(a_n) is a decreasing sequence.

  2. Boundedness: Since an=1n+1a_n = \frac{1}{n+1} is always positive, we know an0a_n \geq 0 for all n1n \geq 1. Therefore, (an)(a_n) is bounded below by 00.

  3. Conclusion: By the Monotone Convergence Theorem, any sequence that is both decreasing and bounded below must converge. Therefore, (an)(a_n) converges.

Part 2: Find the limit of the sequence as nn \to \infty

To find the limit, we examine limnan\lim_{n \to \infty} a_n: limnan=limn1n+1.\lim_{n \to \infty} a_n = \lim_{n \to \infty} \frac{1}{n+1}.

As nn \to \infty, the term n+1n+1 grows indefinitely, causing 1n+1\frac{1}{n+1} to approach 00. Thus, we conclude: limnan=0.\lim_{n \to \infty} a_n = 0.

Part 3: Intuitive Explanation of the Limit

Intuitively, as nn increases, the denominator n+1n+1 in the expression 1n+1\frac{1}{n+1} becomes larger and larger, making the fraction smaller. This trend indicates that each term in the sequence becomes closer to zero as nn grows. The limit of zero aligns with this intuition, as the terms of the sequence approach zero in value as they progress, illustrating a common pattern in sequences where the reciprocal of a linearly increasing term leads to a zero limit.

In summary:

  1. The sequence (an)(a_n) converges because it is decreasing and bounded below.
  2. The limit of (an)(a_n) as nn \to \infty is 00.
  3. Intuitively, this makes sense because the terms get smaller as nn increases due to the growing denominator.

Would you like further clarification on any of these steps?

Here are five related questions that might help deepen your understanding:

  1. Can you prove convergence for other types of sequences, such as (bn)=1n2+1(b_n) = \frac{1}{n^2+1}?
  2. How does the limit of a sequence differ from a limit of a function as xx \to \infty?
  3. What happens if you alter the sequence definition to (cn)=2n+1(c_n) = \frac{2}{n+1}?
  4. Why is the Monotone Convergence Theorem helpful for proving convergence?
  5. How do we approach convergence proofs for non-monotonic sequences?

Tip: In many cases, you can determine a sequence's limit by examining how its formula behaves as nn approaches infinity.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Sequences and Series
Limits
Convergence of Sequences

Formulas

Limit of sequence formula: lim(n→∞) an

Theorems

Monotone Convergence Theorem

Suitable Grade Level

Undergraduate