Need help with calc homework!!
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Need help with calc homework!!

[From: ] [author: ] [Date: 11-12-02] [Hit: ]
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Find the interval and ratio of convergence for this series

sum of (-1)^n (n^2)(x^n)/ 4^n

n = 2 to infinity

Honestly, I'm totally lost. I know a ratio test has to be in there somewhere but I have no clue.
Help please!

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If you know how to do the ratio test its lim n goes to infinity of absolute value(a^n+1)/a^n
When you cross everything out you get x/4((n+1)/n)^2 so you get -1
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The ratio is the formula i mentioned above with the a's it will look like:lim (((-1)^n+1*(n+1)^2(x^(n+1))/4^… (-1)^n (n^2)(x^n)/ 4^n) Kinda hard to type out on the computer but if you can see it the n's cancel and simplify you can write it over each other but i prefer that way. Hope that helps.

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