multinomial therom

$$(x_1+x_2+...+x_t{)}^n=\sum _{k_1+k_2+...+k_t=n}(\genfrac{}{}{0ex}{}{n}{k_1,k_2,...,k_t})\cdot x_1^{k_1}\cdot x_2^{k_2}\cdot ...\cdot x_t^{k_t}$$