How Can I Solve These Sequence Problems Quickly?

  • Thread starter Thread starter rahl__
  • Start date Start date
  • Tags Tags
    Sequences
rahl__
Messages
10
Reaction score
0
i have a few problems with sequences
1. show, that if:
\lim_{n\to\infty}a_{n}=L
than sequence:
b_{n}=\frac{a_{1}+...+a_{n}}{n}
is convergent to L

2. show that the sequencea_{n} is monotone, bounded and find out its limit, if:
a_{1}=2
a_{n+1}=\frac{a_{n}+4}{2}

3. show that if the sequence a_{n} satysfies cauchy's condition than it is convergent.

4. show that there is an inequility :
|\sum_{k=1}^{n}a_{k}b_{k}|\leq\sqrt{\sum_{k=1}^{n}a_{k}^{2}}\sqrt{\sum_{k=1}^{n}b_{k}^{2}}

5. find the limit of such sequence:
a_{n}=(\frac{n+1}{n})^{3n^{2}}

6. find the limit of such sequence:
a_{n}=(\frac{n^{2}+4}{n^{2}+3})^{2n}

7. find the limit of such sequence
a_{n}=-n^{6}+3n^{5}+7

8. find the limit of such sequence
a_{n}=\sqrt[n]{n!}

9. find the limit of such sequence
a_{n}=1+2^{n}-3^{n}

10. a_{n} is a sequence including all rational numbers. show that for each real number M you can find a subsequence of this sequence that is convergent to M

11. a_{n} is a squence, that has a subsequence convergent to \infty and a subsequence convergent to -\infty. show that, if \lim_{n\to\infty}(a_{n}-a_{n-1})=0, than for each real number M there is a subsequence convergent to M.

thanks in advance and sorry for the length of this post, but i really need this answers as soon as possible
 
Last edited:
Physics news on Phys.org
rahl__ said:
thanks in advance and sorry for the length of this post, but i really need this answers as soon as possible
Whoops, sorry, but we are not giving out COMPLETE SOLUTIONS to those who do not even bother to try to find a way to tackle the problem(s). Why must we help him if he shows no interest in finding the solutions on this own? And to remind you, it's your own problems, not ours...
You may want to read the https://www.physicsforums.com/showthread.php?t=28.
Now, may you just show us your works, what have you done to go about tackling the problems? Or at least, some of your thoughts about the problems. And we may help you.
 
Last edited:
you took me wrong, these problems were not my homework exercises. I had an exam last saturday from sequences and multitude theory [?] and from a list of about 100 exercises these 11 were the ones that i had some problems when trying to solve. i thought that this exam will be in 2 weeks time, but it turned out to be on previous saturday so i had very little time to do all those exercises and that's why i have posted just bare examples without my thoughts regarding the possible sollution, its not like I am that lazy or sth.
sorry for creating such confusion
 
Last edited:
I'm sorry rahl, but the https://www.physicsforums.com/showthread.php?t=5374", which you agreed to, says:
On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

So, when you show your efforts, thoughts or any ideas on the problems, people like Vietdao29 and others will gladly assist you.
 
Last edited by a moderator:
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...

Similar threads

Back
Top