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Very quick question

  1. Mar 13, 2008 #1
    Is (3n+3)!=(3n)!+3!
    ? probably obvious but i'm not certain. Trying to work out a radius of convergence for a series.
  2. jcsd
  3. Mar 13, 2008 #2
    No. It is the product from i=1 to 3 of (3n!)*(3n+i)
  4. Mar 13, 2008 #3


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    You can quickly verify this for yourself by checking the case where n = 1.
  5. Mar 13, 2008 #4
  6. Mar 14, 2008 #5
    Ok, this convergence question still has me stuck


    Got the n+1 term and tried dividing the nth term by the nth+1 but does not seem to cancel nicely.
    Last edited: Mar 14, 2008
  7. Mar 14, 2008 #6


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    If [tex]\stackrel{\chi^{n}}{(3n)!}[/tex] is not a fraction with the line missing, then I have no idea what you mean.
  8. Mar 14, 2008 #7
    It is meant to be a fraction, not used to the equation editor software here.
  9. Mar 14, 2008 #8
    Jack - you were on the right track by figuring out the n+1 term. Use the ratio test. You should see fairly readily that the series converges to 0 as n goes to infinity.
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