Question

срооочнооо
дам 100 балов​

Answer 1

Ответ:

$1.A^k_n=\frac{n!}{(n-k)!} \\ C^k_n=\frac{n!}{k!(n-k)!}\\A^3_4-C^2_4=\frac{4!}{(4-3)!}-\frac{4!}{2!(4-2)!}=4!-\frac{4!}{4}=2*3*4-2*3=2*3*3=18$

$2.P_n=n!\\\frac{P_n_+_1}{nP_n_-_2} =\frac{(n+1)!}{n(n-2)!}= \frac{1*2*...*(n-2)(n-1)n(n+1)}{n*1*2...(n-2)} =(n-1)(n+1)=n^2-1$