2. $\sum_{k=0}^{m}$ . $C_{m}^{k}$ . $C_{k+n}^{m}$ = $(-1))^{m}$ . $\sum_{k=0}^{m}$. $C_{m}^{k}$. $C_{n+k}^{k}$ . $(-2)^{k}$
3. $\sum_{k=0}^{p}$. $C_{p}^{k}$ . $C_{q}^{k}$. $C_{n+k}^{p+q}$ = $C_{n}^{p}$ . $C_{n}^{q}$
4. . $\sum_{k=0}^{p}$. $(C_{p}^{k})^{2}$ . $C_{n+2p-k}^{2p}$ = $(C_{n+p}^{p})^{2}$
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