# Binominal help

• Sep 18th 2009, 02:00 AM
helloying
Binominal help
n
c2 = 28

how do i find what is n?
• Sep 18th 2009, 02:04 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.