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Sigma notation and telescopic problem

  1. Nov 20, 2008 #1
    1. The problem statement, all variables and given/known data
    Evaluate the telescoping sum.
    a) Sigma i=1 to n [i^4 - (i - 1)^4]

    2. Relevant equations
    sigma i=1 to n [f(1) - f(i+1)]

    3. The attempt at a solution

    so i plug in for the eqns. and get 1^4 - n^4

    the correct answer should be n^4 but don't know how to get that.
  2. jcsd
  3. Nov 20, 2008 #2


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    You're "relevant equation" doesn't apply to this problem. Just think about it by plugging in the first few terms should be obvious why it's n^4.
  4. Nov 20, 2008 #3
    DO it again, you'll get 0^4 + n^4
  5. Nov 20, 2008 #4


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    Actually, he'll get n^4 - 0^4. Even if they're technically the same thing, you don't want to confuse him more.
  6. Nov 20, 2008 #5
    Righto! I'm sure the poster will get it, just try again carefully.
  7. Nov 21, 2008 #6
    I kinda understand. I see how the first term becomes n^4 but why is the last 0?
  8. Nov 21, 2008 #7


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    Staff Emeritus
    Science Advisor

    Have you actually written down, say, the first 10 terms?
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