# Working with binomial identieies.

chaotixmonjuish
$$\binom{r}{k}=\frac{r}{r-k}\binom{n-1}{k}$$

I'm having problems proving this. However, here is my reasoning:

when factoring out an r you get

$$\frac{r*(r-1)!}{(r-k)!k!}$$
$$\frac{r}{r-k}*\frac{(r-1)!}{(r-k-1)!k!}$$

Is this proper reasoning?