Question

ajutorrrrr,rapiddd,totul scris explicit

Answer 1

$\it c)\ A_n^2\leq3! \Rightarrow \dfrac{n!}{(n-2)!}\leq1\cdot2\cdot3 \Rightarrow \dfrac{(n-2)!\cdot(n-1)\cdot n}{(n-2)!}\leq2\cdot3 \Rightarrow \\ \\ \\ \Rightarrow (n-1)\cdot n\leq2\cdot3 \Rightarrow n\leq3 \ \ \ \ \ \ (1)\\ \\ \\ Dar,\ n\geq2\ \ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow n\in\{2,\ 3\}$