Thread: Combinatorics

Hi,

I need a little bit help with this:

Got to work my way from "sum from k=1 to n (k^2*n nCr k))" to this: (n^2+n)*2^(n-2), but HOW?

I´ve tried god-knows-what but nothing seems to work..

Originally Posted by TempleT

Hi,

I need a little bit help with this:

Got to work my way from "sum from k=1 to n (k^2*n nCr k))" to this: (n^2+n)*2^(n-2), but HOW?

I´ve tried god-knows-what but nothing seems to work..

Did you try calculating it for a couple of different values of n? When n= 1, the sum is . The right side you want to show that equal to is .

You can't prove that, it isn't true.


(Perhaps I am confused as to what "nCr" means. I thought that was the binomial coefficient but there is no "r" on the right, and it isn't an index so I assumed you meant "nCk".)

It it true, that i know for sure. (try wolfram alpha) I do mean the binomial coefficient. I´m from Finland, maybe that is why you are confused with my nCr (we use that)

sum from 0 to n (k^2 (n nCr k)) - Wolfram|Alpha