Wednesday, 10 December 2014

real analysis - Prove the sequence an=fracnnn! is not bounded above



Prove the sequence is an=nnn! not bounded above.




This is exercise 1.4.2 in Introduction to Analysis by Arthur P. Mattuck.



The hint given in the book is "Show that an>n".



I attempted to show this using induction.



Basic Step



a1=111=11




a2=222=22



a3=333=92>3



Inductive Step



Show nnn!>n(n+1)(n+1)(n+1)!>n+1



This is where I get stuck.




I reduced the sequence so (n+1)(n+1)(n+1)!=(n+1)nn!.



I figure the next step is to show (n+1)nn!>nnn!+1, but I am not sure how to get there.



I also looked at this question since it was working with a similar equation, but I wasn't able to derive anything out of the discussion that could lead to an answer.



Edit:



Side Question




Does this need to be solved using induction, or are there other methods of directly proving this result? Is induction a clumsy or unwieldy tool for this problem?


Answer



an=nnn12n=n1n2nn>n1=n


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...