If n is a nonnegative integer and functions f and g have nth-order derivatives, show that:

$\displaystyle (fg)^{(n)}=f^{(n)}g+\left(\begin{array}{ll}n\\1\en d{array}\right)f^{(n-1)}g'+\left(\begin{array}{ll}n\\2\end{array}\right )f^{(n-2)}g''+...+\left(\begin{array}{ll}n\\n\end{array}\ right)fg^{(n)}$

$\displaystyle =\sum_{k=0}^n \left(\begin{array}{ll}n\\k\end{array}\right)f^{(n-k)}g^{(k)}$

Im not well versed in binomial expansion so this is confusing to me