Помогите решить номер 23 а) и в)

A)
$\frac{A_n^7-A_n^9}{A_n^8} = \frac{ \frac{n!}{(n-7)!}- \frac{n!}{(n-9)!} }{ \frac{n!}{(n-8)!} } = \frac{(n-8)!(1-(n-8)(n-7))}{(n-7)!} = \frac{1-n^2+15n-56}{n-7} =\\ = \frac{n^2-15n+55}{7-n}$

в)
$\frac{A_n^3*P_n+2P_{n+1}}{P_{n+1}} = \frac{ \frac{n!}{(n-3)!}*n!+2(n+1)! }{(n+1)!} = \frac{(n-2)(n-1)n+2(n+1)}{n+1} =\\ = \frac{n^3-3n^2+2n+2n+2}{n+1} = \frac{n^3-3n^2+4n+2}{n+1}$