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In the bionomial expansion (1+x)^p

  1. Jul 11, 2010 #1
    In the bionomial expansion (1+x)^p , p can be integer or fraction. The coefficients are written as p
    j . For this to hold p>= j. (j= integer). What happens if p=1/2,-1/2 or any other fraction? How can one use the same combination coefficient formula?

    tks for any hlp.
  2. jcsd
  3. Jul 11, 2010 #2


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    Re: combination

    Is that true?

    As far as I know, you cannot write
    [tex]\sqrt{1 + x} = (1 + x)^{1/2}[/tex]
    [tex]a 1^{1/2} + b x^{1/2} = a + b \sqrt{x}[/tex]
    for any numbers a, b, for example.

    You can write it as
    [tex]\sqrt{1 + x} = a_0 + a_1 x + a_2 x^2 + \cdots[/tex]
    but not with a finite series and an then have little to do with binomial coefficients.

    The fact that it works with integers, is simply because you can open the brackets in, say, (1 + x)n = (1 + x)(1 + x)...(1 + x) [n times], and the coefficient of 1k xn-k is simply the number of ways in which you can choose k of the brackets whose 1 you multiply with the other n - k brackets' x, which is by definition n choose k.
  4. Jul 11, 2010 #3


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    Re: combination

    You need infinitely many terms in that case. Just continue to generate terms the usual way.
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