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Urgent helppp Nth term and sum

  1. Apr 9, 2008 #1
    Ok i have a few here that i have no idea what to do
    b]1. The problem statement, all variables and given/known data[/b]

    Find the nth term in the series
    1/2, 1/3, 2/9, 4/27, 8/81, 16/243

    also

    [tex]\Sigma[/tex] (-1)^n-1/ 5n+1
    find the sum
    Urgent help neededdd ahha.. Thanks
     
  2. jcsd
  3. Apr 9, 2008 #2
    For the first: Try to express the terms as a product of powers of 2 and 3. Biggest hint: 1/2=2^(-1)*3^0. For the second, could you clarify the sum?
     
  4. Apr 9, 2008 #3
    So the 1/2 is just clarifying an alternating series? I am completely lost on that problem. for the second i dunno what you mean either haha... all i know right now is it is an alternating problem... I have been trying to do these for like 3 hours to no success haha..



    edit---
    Well thanks for the first part i figured out the nth term. Im just super slow haha... The second problem however the only info i have oin it is its starts at n=1 the the (-1)^n-1/5n+1 then it asks me to find the sum im pretty sure that all i have
     
    Last edited: Apr 9, 2008
  5. Apr 9, 2008 #4
    Like I said, clarify the sum. Use parentheses and such because I can't make any sense out of what you wrote.
     
  6. Apr 9, 2008 #5
    Re:

    The sequence looks like 2^(n-1) * 3^n starting from 0
     
  7. Apr 9, 2008 #6
    ok starting at n=1 ((-1)^n-1)/(5n+1) so as far as i got is the (-1)^n-1 is pulled out as alternating leaving 1/(5n+1) and they want the sum of that
     
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