Arrangements and Combinations · Identities

Lesson 3

Nikolai Chukhin · Alexander S. Kulikov

Similarly, we can prove a more general statement known as the Vandermonde convolution: \[\sum_{l=0}^{k}\binom{n_1}{l}\binom{n_2}{k-l}=\binom{n_1+n_2}{k}\ .\]