- #1

Physicsissuef

- 908

- 0

## Homework Statement

How is possible this equality:

[tex] {n \choose k} = \frac{n \cdot (n-1) \cdots (n-k+1)}{k(k-1)...1} = \frac{n!}{k!(n-k)!}[/tex]

? I mean where the second part [tex]\frac{n!}{k!(n-k)!}[/tex] comes from?