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Math Help - binomial expansion

  1. #1
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    binomial expansion

    Hi could somebody please help me.
    I really dont understand how to approach this question.

    the coefficient of x^2 is 3/8 in the expansion of (1+x/n)^n. find n.

    any sort of help would be much appreciated.
    thanks.
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  2. #2
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    Quote Originally Posted by wahhdoe View Post
    Hi could somebody please help me.
    I really dont understand how to approach this question.

    the coefficient of x^2 is 3/8 in the expansion of (1+x/n)^n. find n.
    The binomial expansion of \bigl(1+\tfrac xn\bigr)^n is

    \Bigl(1+\frac xn\Bigr)^n = 1 + {n\choose1}\Bigl(\frac xn\Bigr) + {n\choose2}\Bigl(\frac xn\Bigr)^2 + \ldots + \Bigl(\frac xn\Bigr)^n.

    You can see from that what the coefficient of x^2 is (in terms of n). Put it equal to 3/8 and solve for n.
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