Show that a Sequence is monotonically decreasing

In summary, To show that (an) is monotone decreasing given that an = 1/√n, we need to prove that an ≥ an+1. Using the fact that the magnitude of √n+1 is larger than that of √n, we can divide both sides by √n to preserve the inequality and ultimately show that √n+1/√n > 1, which satisfies our requirement.
  • #1
Calu
73
0
Member warned about deleting template parts

Homework Statement



I was wondering how I would go about showing that (an) is monotone decreasing given that an = 1/√n.

I believe I have to show an ≥ an+1, but I'm not sure how to go about doing that.
 
Physics news on Phys.org
  • #2
Calu said:

Homework Statement



I was wondering how I would go about showing that (an) is monotone decreasing given that an = 1/√n.

I believe I have to show an ≥ an+1, but I'm not sure how to go about doing that.

Well, PF rules require you to make a start on your own. What do you know about the magnitudes of ##\sqrt{n}## and ##\sqrt{n+1}##?
 
  • #3
Ray Vickson said:
Well, PF rules require you to make a start on your own. What do you know about the magnitudes of ##\sqrt{n}## and ##\sqrt{n+1}##?
I know that the magnitude of ##\sqrt{n+1}## is larger than that of ##\sqrt{n}##. Therefore I would assume that the opposite would be true for the magnitude of their reciprocals which would make an≥an+1 as required, however I'm not sure how to write this in a more coherent way.
 
  • #4
Calu said:
I know that the magnitude of ##\sqrt{n+1}## is larger than that of ##\sqrt{n}##. Therefore I would assume that the opposite would be true for the magnitude of their reciprocals which would make an≥an+1 as required, however I'm not sure how to write this in a more coherent way.

(1) [itex]\sqrt{n + 1} > \sqrt{n}[/itex].
(2) If [itex]n > 0[/itex] then dividing both sides by [itex]\sqrt{n} > 0[/itex] preserves the inequality. Hence [itex]\frac{\sqrt{n + 1} }{\sqrt{n}} > 1[/itex].
(3) Dividing both sides by ... > 0 preserves the inequality. Hence ...
 

FAQ: Show that a Sequence is monotonically decreasing

1. What does it mean for a sequence to be monotonically decreasing?

A monotonically decreasing sequence is a sequence of numbers where each term is smaller than the previous one. In other words, the terms in the sequence are always getting smaller or staying the same.

2. How do you show that a sequence is monotonically decreasing?

To show that a sequence is monotonically decreasing, you must prove that each term in the sequence is smaller than the previous one. This can be done by using mathematical induction or by finding the difference between consecutive terms and showing that it is always negative.

3. Can a sequence be both monotonically increasing and decreasing?

No, a sequence cannot be both monotonically increasing and decreasing at the same time. If a sequence is monotonically increasing, it means that each term is larger than the previous one, while a monotonically decreasing sequence has each term smaller than the previous one. These two conditions cannot be satisfied at the same time.

4. What is the difference between a monotonically decreasing sequence and a strictly decreasing sequence?

A monotonically decreasing sequence can have consecutive terms that are equal, while a strictly decreasing sequence cannot. In other words, a strictly decreasing sequence is a monotonically decreasing sequence with no repeated terms.

5. Are all monotonically decreasing sequences convergent?

No, not all monotonically decreasing sequences are convergent. A convergent sequence is one that has a limit as the number of terms approaches infinity. A monotonically decreasing sequence can converge or diverge, depending on the values of its terms.

Similar threads

Replies
8
Views
3K
Replies
3
Views
3K
Replies
9
Views
2K
Replies
7
Views
1K
Replies
2
Views
1K
Replies
5
Views
1K
Back
Top