Saturday, 14 February 2015

sequences and series - How do you prove sumfracn2n=2?




How do you prove n=1n2n=2 ?




My attempt: I have been trying to find geometric series that converge to 2 which can bind the given series on either side. But I am unable to find these. Is there a general technique to find the sum? This is a high school interview question and must be easy enough to solve in a few minutes.



Please give any hints for the first step towards a solution.


Answer



Hint: Denote your sum by S, rewrite S=2SS and try to rewrite the sums.


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