Proving a summation involving binomial coefficients. I need to prove the following inductively: (http://upload.wikimedia.org/math/9/e/5/9e57871ba17c1ad48e01beb7e1bb3bb9.png)
$$\sum_{i=1}^{n} i{n \choose i} = n2^{n-1}$$
And for the life of me I can't figure out how to express the formula with n+1 in terms of n.

** I was going to withdraw this answer as it does not use induction, but decided to leave it anyway and take the criticism. Thanks lab bhattacharjee for setting me right** 
Start with
$$
(x+1)^n = \sum _i {n \choose i} x^i
$$
and differentiate with respect to $x$
$$
n(x+1)^{n-1} = \sum _i  {n \choose i} i  x^{i-1}
$$
Now set $x=1$ to get your identity
$$
n ~2^{n-1} = \sum _i  i~ {n \choose i} 
$$
