Tuesday, 29 December 2015

calculus - Partial sum of divergent series



I am trying to find the nth partial sum of this series:
S(n)=2(n+1)2




I found the answer on WolframAlpha:



mn=0(1+2n)2=13(m+1)(2m+1)(2m+3)



How can I calculate that sum, without any software?


Answer



S(n)=(1+2n)2=1+4n+4n2
You can now use the following mn=01=m+1mn=0n=m(m+1)2mn=0n2=m(m+1)(2m+1)6




Alternatively, compute the first 4-5 elements. The sum of a polynomial of order p will be a polynomial of order p+1 in the number of terms. Find the coefficients, then prove by induction


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