
#1
September 10th, 2015,
15:15
Let $\left\{{a}_{n}\right\}$ be a nonnegative, nonincreasing sequence and convergence to $a \ge 0$. Can we say that ${a}_{n}\ge a$ for all n $\in \Bbb{N}$ ?
Also, if $\left\{{a}_{n}\right\}$ is a nonnegative, decreasing sequence and convergence to $a \ge 0$. Can we say that ${a}_{n}> a$ for all n $\in \Bbb{N}$ ?

September 10th, 2015 15:15
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MHB Master
#2
September 10th, 2015,
16:41
Originally Posted by
ozkan12
Let $\left\{{a}_{n}\right\}$ be a nonnegative, nonincreasing sequence and convergence to $a \ge 0$. Can we say that ${a}_{n}\ge a$ for all n $\in \Bbb{N}$ ?
Also, if $\left\{{a}_{n}\right\}$ is a nonnegative, decreasing sequence and convergence to $a \ge 0$. Can we say that ${a}_{n}> a$ for all n $\in \Bbb{N}$ ?
Hi ozkan12,
Let me give you a hint for the first part. Consider the sequence,
\[\left\{a_n\right\}_{n=1}^{\infty}=\left\{1+\frac{(1)^n}{n}\right\}_{n=1}^{\infty}\]

#3
September 10th, 2015,
17:02
Thread Author
İs this sequence convergent ?

MHB Master
#4
September 10th, 2015,
18:19
Originally Posted by
ozkan12
İs this sequence convergent ?
Take the limit of the sequence,
\[\lim_{n\rightarrow\infty}\left(1+\frac{(1)^n}{n}\right)=\lim_{n\rightarrow\infty}1+\lim_{n\rightarrow\infty}\frac{(1)^n}{n}=1+\lim_{n\rightarrow\infty}\frac{(1)^n}{n}\]
What does that equal to?

#5
September 11th, 2015,
03:20
Thread Author
limit of sequence equal to 1, but this sequence is not nonincreasing...
Last edited by ozkan12; September 11th, 2015 at 03:26.

MHB Master
#6
September 11th, 2015,
08:39
Originally Posted by
ozkan12
limit of sequence equal to 1, but this sequence is not nonincreasing...
Hi ozakn12,
I guess this depends on what you mean by nonincreasing. I took it as a sequence that is not increasing. For an each term should be greater than the one before it. Hence this sequence is nonincreasing.
The first few terms of the sequence are, $\left\{0,\frac{3}{2},\frac{2}{3},\frac{5}{4},\frac{4}{5},\frac{7}{6},\frac{6}{7},\ldots\right\}$

#7
September 11th, 2015,
08:46
Thread Author
Dear,
I dont understand, what you say...Can you explain my question ? Because your hint is very strange for me, İn most source, I see definition of increasing, non increasing, not increasing, decreasing, non decreasing vs......And there are very difference between these definitions....Therefore, I didnt understand these definitions...Can you explain my questions without any example...

MHB Master
#8
September 11th, 2015,
10:23
Originally Posted by
ozkan12
Dear,
I dont understand, what you say...Can you explain my question ? Because your hint is very strange for me, İn most source, I see definition of increasing, non increasing, not increasing, decreasing, non decreasing vs......And there are very difference between these definitions....Therefore, I didnt understand these definitions...Can you explain my questions without any example...
I guess first we need to get the definitions cleared out. It is true that the definitions can have minor differences according to what source you refer. Did you learn about sequences in school/university? If so could you please write down your definitions for increasing and decreasing sequences or point me to a specific source where you learnt these?

#9
September 11th, 2015,
11:42
Thread Author
Dear,
I learnt these definitions from internet, some analysis book etc...I didnt decide that which is true ?
And which is true for nonincreasing $\left\{{a}_{n}\right\}$ sequence which is convergent to nonnegative $p\ge 0$.
${a}_{n} \ge p$ for all $n\in \Bbb{N}$ or ${a}_{n} > p$ for all $n\in \Bbb{N}$. Which is true ?

MHB Master
#10
September 11th, 2015,
11:48
Originally Posted by
ozkan12
Dear,
I learnt these definitions from internet, some analysis book etc...I didnt decide that which is true ?
And which is true for nonincreasing $\left\{{a}_{n}\right\}$ sequence which is convergent to nonnegative $p\ge 0$.
${a}_{n} \ge p$ for all $n\in \Bbb{N}$ or ${a}_{n} > p$ for all $n\in \Bbb{N}$. Which is true ?
Refer one specific source, so that you don't get mixed up with the definitions. A good source of reference to learn about the basic definitions of sequences is .