- #1
Muradean
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1. The problem:
Ive been all afternoon struggling with this doubt. Its a bit more teoric than the rest of the exercices i did and i just can't seem to get around it so here it goes :
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Consider ∑ 1/an a convergent serie of positive terms.
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What´s the nature of Σ (-1)^n/(an^(2) +1)
(Leibniz criterion) ? If ∑(-1)^(n)an is an alternated serie and the sucession(an) is decreasing and his limit→+00 an = 0 then i can say that ∑(-1)^(n)an is converging.
My initial thought was:... a-ha! This is an alternate serie! Because of the (-1)^n ...
So if i prove that the serie 1/an is decreasing since i already know the lim an= 0 i can say that the serie:
(Leibniz criterion)
Σ (-1)^n/(an) IS CONVERGENT however i have two problems...1- I don't know how to prove that 1/an is decreasing.
2- The serie that they ask me to study is different and even if i could prove that 1/an is decreasing i don't know if through algebric manipulation i could get to:
Σ (-1)^n/(an^(2) +1)
Im not even sure if I am going the right way. Anyone has any clue? This is bothering me so much!atement, all variables and given/known data
Ive been all afternoon struggling with this doubt. Its a bit more teoric than the rest of the exercices i did and i just can't seem to get around it so here it goes :
--------------------------------------------------------------------------------------------------------------------------------
Consider ∑ 1/an a convergent serie of positive terms.
--------------------------------------------------------------------------------------------------------------------------------
What´s the nature of Σ (-1)^n/(an^(2) +1)
Homework Equations
(Leibniz criterion) ? If ∑(-1)^(n)an is an alternated serie and the sucession(an) is decreasing and his limit→+00 an = 0 then i can say that ∑(-1)^(n)an is converging.
The Attempt at a Solution
My initial thought was:... a-ha! This is an alternate serie! Because of the (-1)^n ...
So if i prove that the serie 1/an is decreasing since i already know the lim an= 0 i can say that the serie:
(Leibniz criterion)
Σ (-1)^n/(an) IS CONVERGENT however i have two problems...1- I don't know how to prove that 1/an is decreasing.
2- The serie that they ask me to study is different and even if i could prove that 1/an is decreasing i don't know if through algebric manipulation i could get to:
Σ (-1)^n/(an^(2) +1)
Im not even sure if I am going the right way. Anyone has any clue? This is bothering me so much!atement, all variables and given/known data
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