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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- Feb 2nd 2010, 08:06 AMwahhdoebinomial 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. - Feb 2nd 2010, 08:34 AMOpalg
The binomial expansion of $\displaystyle \bigl(1+\tfrac xn\bigr)^n$ is

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

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