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posted by  alexia on 10/31/2009 10:46:09 PM  |  status: Closed  |  Earned Karma: 50

series

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Calculus N/A N/A N/A 11/1/2009 at 7:00:00 AM
Question Details:
 determine if the series converge or diverge using an appropiate test.

  ∞
  ?      2^n - 5^n+1
 n=1          6^n
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posted by zsm28 on 10/31/2009 11:08:53 PM  |  status: Live
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Response Details:
  ∞
 Σ      2^n - 5^n+1
n=1          6^n
=
Σ(2/6)n - Σ(5/6)n + Σ(1/6)nn
All these three series are geometric with common ratio 2/6, 5/6 and 1/6 respectively, all these ratios are < 1, so the original series is convergent.
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posted by hado on 10/31/2009 11:11:53 PM  |  status: Live
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Response Details:

                           
The first series is geometric series with common ratio r=1/3<1 ==> it is convergent
The second series is geometric series with common ratio r=5/6<1 ==> it is convergent
The third series is geometric series with common ratio r=1/6<1 ==> it is convergent
==>

Therefore, we conclude that the given series converges, since it is the sum of three convergent series.

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posted by Paul K on 10/31/2009 11:55:13 PM  |  status: Live
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Response Details:
     Given:
Question Details:
 determine if the series converge or diverge using an appropiate test.

  ∞
  ?      2^n - 5^n+1
 n=1          6^n
   
                               
                               .
I will show that the series converges by the integral test :
                                                           
                                                           
                           
                                                            
                                                            .
We thus have the integral converges . We therefore have by the integral test that the series also .
We also have :
.
The series is thus the sum of three geometric series which converge :
      ----    and ; so , the series converges to :
.
     -----   and  ; so , the series converges to :
.
  -----    and  ; so , the series converges to :
. We thus have the series is the sum of three convergent geometric series :
.
      
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posted by alexia on 11/1/2009 7:35:43 AM  |  status: Live
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Response Details:
it looks you interpreted the question wrong the 5 in the question is not only to the power of n, its to the power of n+1.
the n+1 should have been in parenthesis.
Thanks,
Alexia
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posted by sai swaroop on 11/1/2009 8:16:01 AM  |  status: Live
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-- sai swaroop "If there is no struggle, there is no progress"
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