Do these converge absolutely, conditionally, or diverge?

sigma from n = 1 to infinity of (n + 1)^2 / n!

sigma from n = 1 to infinity of (1/ (arctan(n))^(2n)

explain please!

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- November 28th 2010, 07:35 PMPlaythiousNeed help with these convergence Tests?
Do these converge absolutely, conditionally, or diverge?

sigma from n = 1 to infinity of (n + 1)^2 / n!

sigma from n = 1 to infinity of (1/ (arctan(n))^(2n)

explain please! - November 28th 2010, 07:38 PMdwsmith
I first break it up. (n+1)^2=n^2+2n+1

Now you can evaluate three separate Summations.

I think the 2nd one can be evaluate like a geometric since ArcTan(Infinity)=pi/2 - November 28th 2010, 07:39 PMProve It
For the first, try the ratio test.

Evaluate . If this is the series converges absolutely, if this is the series diverges. If this the test is inconclusive. - November 28th 2010, 08:08 PMPlaythious
so for the first one I applied the ratio test and got

lim (as n goes to infinity) of (n^2 + 2n + 1) / ( (n+1)(n^2) ) + lim (as n goes to infinity) (2n + 1)/( (n+1)(n^2) + lim (as n goes to infinity) of 1/(n+1)

and since all of these go to zero then the sum converges absolutely?

and for the second one you have

sum (from 1 to infinity) 1 / (pi/2)^2n

and because pi/2 is greater than 1 it just diverges by geometric series test? - November 28th 2010, 08:14 PMdwsmith
You are mixing up two separate suggestions. I thought you wanted to solve the series but you just want to know if they converge. Just follow Post #3

- November 28th 2010, 08:19 PMPlaythious
ahh i see

so lim (as n goes to infinity) (n+2)^2 / ( (n+1)(n+1)2 which is just 0 so it converges abs

what about the second one? - November 28th 2010, 09:36 PMdwsmith
Try the nth root test