# Math Help - Calculate this sum

1. ## Calculate this sum

Calculate :
$S = \sum\limits_{p = 0}^n {C_p^n p^2 } \left( { - 3} \right)^p
$

2. Start with the binomial expansion $(1+x)^n = \sum_{p=0}^n{n\choose p}x^p$. Differentiate, multiply by x, differentiate again, multiply by x again, then put x=–3.