1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Not able to simplify this summation formula?

  1. Jan 10, 2014 #1

    Please see the attached pdf file. Equation 1 and equation 2 are equivalent.
    Can someone please help me understand how to simplify equation 1 to get to equation 2?


    Attached Files:

    Last edited: Jan 10, 2014
  2. jcsd
  3. Jan 10, 2014 #2


    User Avatar
    Homework Helper

    The summation variable is n, so x can be considered a constant hence it can be pulled out the front.

    What is


    equal to?
  4. Jan 10, 2014 #3
    Please see the new attached file.
    This is how far I could go.

    Attached Files:

  5. Jan 10, 2014 #4


    User Avatar
    Science Advisor

    The point is that both of your series are geometric series. What you do in your last post is essentially repeating the proof that the sum of the geometric series, [itex]\sum_{n=0}^\infty r^n[/itex] is [itex]\frac{1}{1- r}[/itex] except that you have [itex]r= \frac{1}{\gamma}[/itex].
  6. Jan 10, 2014 #5


    User Avatar
    Homework Helper

    There is no mention of infinite sums.

    musicgold, so what is


    And hence, let n=10. Also,


    Can be simplified further. At least get rid of the fraction within the denominator.
  7. Jan 10, 2014 #6
    Please see the attached file.

    I think, I am close, but not sure how to get rid of the 'y' in the encircled term.
    What am I missing?

    Attached Files:

  8. Jan 10, 2014 #7


    User Avatar
    Homework Helper

    Sorry, this was supposed to be


    We're looking for


    while you're finding


    In your second attachment when you found


    You began the sum with n=0 when you should've began with n=1.
  9. Jan 15, 2014 #8

    Yes. I was able to solve it with that correction. See attached. Thank you very much.

    Attached Files:

  10. Jan 16, 2014 #9


    User Avatar
    Homework Helper

    Good work :smile:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted