# Prove the identity using a combinatorial proof

• Apr 7th 2011, 06:49 AM
apple2009
Prove the identity using a combinatorial proof
Prove the identity

$\displaystyle \sum_{k=0}^{n} k {n \choose k} = n 2^{n-1}$
• Apr 7th 2011, 09:38 AM
veileen
Uhm, what did you try to do?
• Apr 7th 2011, 11:12 AM
apple2009
I try to use a combinatorial proof that both side of the equation count the same thing.
Because I don't know how to try the equation, so I insert the image of it here. (785091c89b91773535544515523d773b.png)
• Apr 7th 2011, 11:25 AM
veileen