Negated Upper Index of Binomial Coefficient/Corollary 1

Corollary to Negated Upper Index of Binomial Coefficient
Let $r \in \R, k \in \Z$.

Then:
 * $\dbinom {-r} k = \paren {-1}^k \dbinom {r + k - 1} k$

where $\dbinom {-r} k$ is a binomial coefficient.