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Sequences - factorial r, !

  1. Nov 14, 2003 #1
    Can anybody help me solving this?

    Write in terms of factorials

    n((n^2)-1)

    The correct answer is
    (n+1)!/(n-2)!

    but I don't know how to get there, and since it's week- end I have no chance to ask anyone teachers, etc.
    //Martin
     
  2. jcsd
  3. Nov 14, 2003 #2
    n(n2-1) = n(n-1)(n+1)
     
  4. Nov 14, 2003 #3
     
  5. Nov 14, 2003 #4

    Tom Mattson

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    Staff Emeritus
    Science Advisor
    Gold Member

    I'll give you a hint.

    Expand the numerator and denominator of the above ratio and cancel the factors common to both. For instance, the numerator is:

    (n+1)!=(n+1)(n)(n-1)(n-2)...

    Get the idea?
     
  6. Nov 14, 2003 #5
    Yes!:smile:
    Thank you!

    //Martin
     
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