Номер 327(а) пожалуйста!!!!!!!

[latex]A^{n+2}_{k+n}+A^{n+1}_{k+n}= \frac{(k+n)!}{(k+n-n-2)!}+ \frac{(k+n)!}{(k+n-n-1)!}= (k+n)!( \frac{1}{(k-2)!}+ \frac{1}{(k-1)!})= \\ \\ =(k+n)!( \frac{k-1}{(k-2)!(k-1)}+ \frac{1}{(k-1)!})=(k+n)!( \frac{k-1}{(k-1)!}+ \frac{1}{(k-1)!})= \\ \\ =(k+n)!( \frac{k-1+1}{(k-1)!} ) =(k+n)!\cdot \frac{k}{(k-1)!} [/latex] [latex]A^{n}_{k+n}= \frac{(k+n)!}{(k+n-n)!}=\frac{(k+n)!}{k!}[/latex] [latex](k+n)!\cdot \frac{k}{(k-1)!} : \frac{(k+n)!}{k!}=(k+n)!\cdot \frac{k}{(k-1)!}\cdot \frac{k!}{(k+n)!}=k^2[/latex]