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Infinite geometric series problem

  1. Oct 7, 2010 #1
    1. The problem statement, all variables and given/known data

    [tex] \sum_{n=1}^\infty \frac{(-3)^{n-1}}{4^n} [/tex]

    3. The attempt at a solution

    [tex] \sum_{n=1}^\infty \frac{(-3)^n-1}{4^n} [/tex]

    [tex] \frac{1}{4}\sum_{n=1}^\infty \frac(-{3}{4})^{n-1} [/tex]

    Can some one please explain how they got from the first step to the 2nd. How do you pull out a 1/4 and how does the "n" on the 4 dissapear?
  2. jcsd
  3. Oct 7, 2010 #2


    Staff: Mentor

    Can you fix your third summation? It's all fouled up.
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