Chu-Vandermonde Identity/Examples/2 from e + pi

Example of Use of Chu-Vandermonde Identity
Let $r = e$, $s = \pi$ and $n = 2$


 * $\ds \binom {e + \pi} 2 = \sum_{k \mathop = 0}^2 \binom e k \binom \pi {2 - k}$