I am trying to prove that (sn) is a Cauchy sequence where |sn+1-sn| < 2-n.
So far, I have figured out that |sm-sn| <= 1/2m+1 + 1/2m+2 + ... + 1/2n. I want to try to not use the geometric series condition. My professor hinted that the right hand side is less than 2/2n but I'm not sure how to find that or how to go from here!
Note. I'm not sure what is meant by |sn+1-sn|< 2-n. According to my judgement, it might be
Case 1. , in which case the solution is given below.
Case 2. , in this case {} is not a Cauchy sequence at all. Suitable counter example is given.
Case 3. , which is not possible as for n > 2, it would imply that a non negative number is less than 0, which is certainly not possible.
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