Friday, 9 October 2015

real analysis - Two sequences, one of them bounds difference of the other and converges to 0. Show that the other sequence converges.



That is, let (an)n=1 and (bn)n=1 be sequences such that bnn0 and for all kN and lk,
|alak|<bk.
Show that (an)n=1 is Cauchy.



My guess is that an0. So, we could try working from the definition of convergence and show that an0, but it isn't clear to me how to show that |an|<ϵ.




Hints, not complete solutions, are appreciated.



Edit: Could the squeeze theorem potentially be useful here?


Answer



Hint: Let ϵ>0. Then there exists N such that bn<ϵ for nN. What happens if k,lN?


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