Calculate the sum of the series

  • Thread starter shemer77
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  • #1
shemer77
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so i am having trouble calculating the sum of the series of
(1+2^x)/(3^x) from 1 to infinity
i rearranged it and made a geometric series where r =2/3 and got that it converges toward 2. however the answer is 2.5? This problem shouldn't need any tests as its it a section of the book that hasant taught any of the tests, except for geometric so what am I doing wrong. I have been stuck on this for hours now? :(
 

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  • #2
SammyS
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Let's see details for how you went about getting your result.
 
  • #3
Bohrok
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so i am having trouble calculating the sum of the series of
(1+2^x)/(3^x) from 1 to infinity
i rearranged it and made a geometric series where r =2/3 and got that it converges toward 2. however the answer is 2.5? This problem shouldn't need any tests as its it a section of the book that hasant taught any of the tests, except for geometric so what am I doing wrong. I have been stuck on this for hours now? :(

You forgot about the 1 in the numerator:

[tex]\sum \frac{1 + 2^x}{3^x} = \sum \left(\frac{1}{3^x} + \frac{2^x}{3^x} \right) = \sum \frac{1}{3^x} + \sum \left(\frac{2}{3}\right)^x = ?[/tex]
 
  • #4
nickalh
72
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Borhok has the right method again.
Shemer77, would you let us know if you've gotten the right answer from Bohrok's information or still have further questions? Thanks.
 

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