Thursday, July 11, 2019

real analysis - How do I show a sequence is bounded, use for one part of the monotone convergence theorem?



So the monotone convergence theorem states that if a sequence is bounded and monotone then it converges.



Now I am trying to prove that the sequence defined recursively as x1=2, xn+1=2xn converges and to find it's limit.



I am able to show that the sequence is monotone by determining if the ratio of xn+1xn is greater than and equal to or less than or equal to 1. I am even know what the limit is.



My dilemma is I am not sure how to determine if this sequence is bounded and I am not quite sure what I need to do to show that its bounded. Can anyone offer a few hints or strategies? I know that it is bounded below by 2; however the sequence is increasing so I need to show that there is an upperbound as well.


Answer




Hint: Use Induction. Suppose xn<2, what can you say about xn+1?


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