# Binominal help

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• September 18th 2009, 03:00 AM
helloying
Binominal help
n
c2 = 28

how do i find what is n?
• September 18th 2009, 03:04 AM
red_dog
$C_n^2=\frac{n(n-1)}{2}$

Then $\frac{n(n-1)}{2}=28\Rightarrow n^2-n-56=0$

Now solve the quadratic and choose the positive integer solution.