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Timeline for Convergence of a series

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Aug 8, 2016 at 7:15 comment added Deepti @Anton: Maybe, this is a bit shorter version of your proof. Set $S_0:=0,$ in addition to $S_N, N\geq 1$ defined previously. Correspondingly, $T_0= -ab_0.$ Then $\sum_{j=0}^Ma^jT_j=-a^{M+1}S_{M+1}.$ As $M\to \infty,$ then the left-hand side tends to $F(a)=0$ (this was asked by Alexandre Eremenko), whence $\{a^jS_j\}\to 0$ and we obtain $F_N=S_N.$ And then your reasoning on the Cauchy sequence. Thank you so much for your interest in the question and nice solution, Deepti.
Aug 4, 2016 at 12:44 history edited user1688 CC BY-SA 3.0
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Aug 4, 2016 at 12:38 comment added user1688 @Deepti: it does, however it can be repaired and I did so.
Aug 4, 2016 at 12:37 history edited user1688 CC BY-SA 3.0
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Aug 4, 2016 at 10:00 comment added Deepti @Anton: Does it matter that the limit $A$ depends on $N$?
Aug 4, 2016 at 8:07 history edited user1688 CC BY-SA 3.0
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Aug 4, 2016 at 7:56 comment added user1688 @Alexandre Eremenko: In the definition of $F(z)$.
Aug 4, 2016 at 7:41 comment added Alexandre Eremenko @Anton: Where does your proof use that $F(a)=0$ ? It is clear that the statement does not hold without this assumption.
Aug 4, 2016 at 7:01 history edited user1688 CC BY-SA 3.0
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Aug 4, 2016 at 6:29 comment added Deepti I think there is a small misprint: it should be $S_N-a^{M+1}S_{N+M+1} $ in the formula for the sum $\sum_{j=0}^M a^jT_{N+j}.$
Aug 4, 2016 at 6:25 vote accept Deepti
Aug 3, 2016 at 20:05 history edited user1688 CC BY-SA 3.0
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Aug 3, 2016 at 17:05 history edited user1688 CC BY-SA 3.0
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Aug 3, 2016 at 16:48 history undeleted user1688
Aug 3, 2016 at 16:48 history edited user1688 CC BY-SA 3.0
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Aug 3, 2016 at 16:15 history deleted user1688 via Vote
Aug 3, 2016 at 16:10 history answered user1688 CC BY-SA 3.0