i'm having a problem proving raabe's criteria for convergent sums.(adsbygoogle = window.adsbygoogle || []).push({});

here in planetmath there's a description of it:

http://planetmath.org/encyclopedia/RaabesCriteria.html

i got that the first inequality is correct when mu is smaller than 1.

i got a hint in my test that i should show that {na_(n+1)} is monotonely decreasing, which i did and by another theorem to show c_n=(n-1)a_n-na_(n+1) is convergent which i also did, but i got that

(1-a_(n+1)/a_n)*n=(1-(1-1/n))*n=1>=mu.

where have i gone wrong?

thanks in advance.

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# Raabe's criteria

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