Real Analysis: Sequences and Series

In summary, the conversation discusses proving that for every k in the natural numbers, a decreasing sequence (ak) that approaches 0 is greater than or equal to 0. The suggestion is to use an indirect argument and assume ak < 0.
  • #1
sprstph14
3
0
Suppose that ak is a decreasing sequence and (ak) approaches 0. Prove that for every k in the natural numbers, ak is greater than or equal to 0.

I was thinking I should assume the sequence is bounded below by 0 and do a proof by contradiction.

Any suggestions?
 
Physics news on Phys.org
  • #2
sprstph14 said:
Suppose that ak is a decreasing sequence and (ak) approaches 0. Prove that for every k in the natural numbers, ak is greater than or equal to 0.

I was thinking I should assume the sequence is bounded below by 0 and do a proof by contradiction.

Any suggestions?

If you assume the sequence is bounded below by 0 you are assuming what you are trying to prove.

Just try an indirect argument. Assume some ak < 0. You should be able to get an easy contradiction.
 
  • #3
thanks. I guess I just really don't know what I'm doing.
 

Related to Real Analysis: Sequences and Series

1. What is a sequence in real analysis?

A sequence in real analysis is a list of numbers that are arranged in a specific order. It is denoted by {an} or (an) and each number in the sequence is represented by the subscript n. The order of the numbers is important and can be infinite.

2. What is a convergent sequence in real analysis?

A convergent sequence in real analysis is a sequence in which the terms get closer and closer to a specific limit as n approaches infinity. This limit is known as the limit of the sequence and is denoted by lim an = L. In other words, the terms of the sequence approach a specific value as n gets larger.

3. What is a divergent sequence in real analysis?

A divergent sequence in real analysis is a sequence in which the terms do not approach a specific limit as n approaches infinity. This means that the terms of the sequence either increase or decrease without approaching a specific value. Divergent sequences can be either unbounded or oscillating.

4. How do you test for convergence or divergence of a series in real analysis?

To test for convergence or divergence of a series in real analysis, you can use various tests such as the ratio test, the root test, or the comparison test. These tests compare the series to a known series with known convergence or divergence properties to determine if the series in question also converges or diverges.

5. What is the difference between a sequence and a series in real analysis?

A sequence is a list of numbers arranged in a specific order, while a series is the sum of the terms in a sequence. In other words, a series is the result of adding up all the terms in a sequence. While a sequence can be convergent or divergent, a series is said to be convergent if its corresponding sequence is convergent.

Similar threads

  • Calculus and Beyond Homework Help
Replies
1
Views
353
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
13
Views
987
  • Calculus and Beyond Homework Help
Replies
8
Views
2K
  • Calculus and Beyond Homework Help
Replies
8
Views
2K
  • Calculus and Beyond Homework Help
Replies
2
Views
144
Replies
1
Views
594
  • Calculus and Beyond Homework Help
Replies
5
Views
2K
  • Calculus and Beyond Homework Help
Replies
1
Views
736
  • Calculus and Beyond Homework Help
Replies
1
Views
1K
Back
Top