lean_workbook_plus_49156

Prove that: \n $1) \binom{n}{m} \binom{n-m}{n-2m}= \binom{n}{2m} \binom{2m}{n}$ ; \n $2) 1!\cdot0+2!\cdot1^2+3!\cdot2^2+...+n!\cdot(n-1)^2=(n+1)!\cdot(n-2)+2$ .