Multinomial theorem
= Multinomial theorem
{wiki}
For a nonnegative integer $n$,
$$
(x_1+\cdots+x_r)^n
=\sum_{\alpha_1+\cdots+\alpha_r=n}
\frac{n!}{\alpha_1!\cdots\alpha_r!}
x_1^{\alpha_1}\cdots x_r^{\alpha_r}.
$$
= Multinomial theorem
{wiki}
For a nonnegative integer $n$,
$$
(x_1+\cdots+x_r)^n
=\sum_{\alpha_1+\cdots+\alpha_r=n}
\frac{n!}{\alpha_1!\cdots\alpha_r!}
x_1^{\alpha_1}\cdots x_r^{\alpha_r}.
$$