Math Help - n choose k

1. n choose k

n chooses k n on top k below in brackets
what that means

like 75 on top 3 below in brackets

2. Originally Posted by math321
n chooses k n on top k below in brackets
what that means

like 75 on top 3 below in brackets
Surely it is defined in your textbook or class notes! Out of interest, where have you met this notation ....?

3. $\binom{n}{k}=\frac{n!}{(n-k)!k!}$

$\binom{75}{3}=\frac{75!}{(72)!3!}$

4. Originally Posted by math321
n chooses k n on top k below in brackets
what that means like 75 on top 3 below in brackets
Do you mean this
$\left\{ {\begin{array}{*{20}c} n \\ k \\ \end{array} } \right\}$ and not $\binom{n}{k}~?$