1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Convergence of series

  1. Oct 12, 2005 #1
    i have the following series from 1 to infinity:
    [tex]\sum(-1)^{n-1}*(\frac{4^n}{7^n})[/tex]
    how can i evaluate the sum of this?
    thanks
    i know the answer is 4/11 but i do not know how to get this.
     
  2. jcsd
  3. Oct 12, 2005 #2

    quasar987

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Look closer; it's just a geometrical serie.

    What you might have missed: [itex](-1)^{n-1}=(-1)^{n+1}[/itex].
     
  4. Oct 12, 2005 #3
    how does this fact help me find what the sum is equal to?
     
  5. Oct 13, 2005 #4

    quasar987

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  6. Oct 13, 2005 #5

    Pyrrhus

    User Avatar
    Homework Helper

    It's like quasar said you need to rewrite into the form

    [tex] \sum_{n=0}^{\infty} ar^n = \frac{a}{1-r}[/tex]

    where

    [tex] a \neq 0 [/tex]
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Convergence of series
  1. Series Convergence (Replies: 3)

  2. Convergence of series (Replies: 2)

  3. Series convergence (Replies: 26)

  4. Convergence of a series (Replies: 24)

  5. Series Convergence (Replies: 15)

Loading...