Math Problem Statement

Afgør om talfølgen: a_n = (n+1/2n)(1 - 1/n) konvergerer eller divergerer. I tilfælde af konvergens, find grænseværdien.

Solution

The problem asks to determine whether the sequence an=(n+12n)(11n)a_n = \left(\frac{n+1}{2n}\right)\left(1 - \frac{1}{n}\right) converges or diverges. If it converges, we need to find the limit.

Step 1: Simplify the expression

We begin by simplifying ana_n: an=(n+12n)(11n)a_n = \left(\frac{n+1}{2n}\right)\left(1 - \frac{1}{n}\right)

Let's simplify each part:

  • n+12n=n2n+12n=12+12n\frac{n+1}{2n} = \frac{n}{2n} + \frac{1}{2n} = \frac{1}{2} + \frac{1}{2n}
  • 11n1 - \frac{1}{n} is already simplified.

Now substitute these into the expression for ana_n: an=(12+12n)(11n)a_n = \left(\frac{1}{2} + \frac{1}{2n}\right)\left(1 - \frac{1}{n}\right) Expanding this product: an=(12+12n)(11n)=12(11n)+12n(11n)a_n = \left(\frac{1}{2} + \frac{1}{2n}\right)\left(1 - \frac{1}{n}\right) = \frac{1}{2}\left(1 - \frac{1}{n}\right) + \frac{1}{2n}\left(1 - \frac{1}{n}\right)

Now, expand each term: an=1212n+12n12n2a_n = \frac{1}{2} - \frac{1}{2n} + \frac{1}{2n} - \frac{1}{2n^2}

Simplifying the expression: an=1212n2a_n = \frac{1}{2} - \frac{1}{2n^2}

Step 2: Find the limit

Now, we evaluate the limit of ana_n as nn \to \infty: limnan=limn(1212n2)=120=12\lim_{n \to \infty} a_n = \lim_{n \to \infty} \left(\frac{1}{2} - \frac{1}{2n^2}\right) = \frac{1}{2} - 0 = \frac{1}{2}

Conclusion

The sequence ana_n converges, and its limit is: limnan=12\lim_{n \to \infty} a_n = \frac{1}{2}

Would you like further details on any part of the solution or have any questions?

Here are 5 related questions to expand on this concept:

  1. How can you prove that a sequence diverges using limits?
  2. What is the difference between absolute and conditional convergence for series?
  3. How can L'Hôpital's Rule be applied to sequences?
  4. Can we determine the speed of convergence for the sequence ana_n?
  5. How does the behavior of a sequence relate to the properties of its corresponding series?

Tip: When simplifying sequences, factor as much as possible to clearly see terms that approach zero as nn \to \infty.

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

Formulas

a_n = (n+1)/(2n) * (1 - 1/n)
lim_{n \to \infty} a_n

Theorems

Limit of a Sequence

Suitable Grade Level

Grades 11-12