Show that: $\left(\begin{array}{l}n \\ r\end{array}\right)$ is given by the recursion formula
$$\left(\begin{array}{l}n \\r\end{array}\right)=\frac{n-r+1}{r}\left(\begin{array}{c}n \\r-1\end{array}\right)$$
where $\left(\begin{array}{l}n \\ 0\end{array}\right)=1$