Thursday, 8 January 2015

Divergence or convergence of a sin series




n=1nsin(nπ2)n2+12



Calc noob here.
I have this series. From inputting the first few values I realize this is an alternating series. I also knew this as sin is alternating. From seeing the pattern I tried to solve this series by changing the sum to:



n=1(2n1)(1)n+18n+5



The first few values are: 1/13 - 3/21 + 5/37 - 7/61 +...



I'm not sure if this is a valid move.

I believe my second sum diverges. As we find from the series divergence test that the limit would not equal 0.



Any help is appreciated!


Answer



n=1nsin(πn2)n2+12=n=0(1)n(2n+1)(2n+1)2+12 The series converges by alternating series test.


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