Răspuns:
[tex]\frac{4*(n+4)!}{2*n!}=\frac{(n+5)!}{(n+1)!},~2*\frac{(n+1)!}{n!} =\frac{(n+5)!}{(n+4)!},~2*\frac{n!*(n+1)}{n!}=\frac{(n+4)!*(n+5)}{(n+4)!},~2*(n+1)=n+5,~2n+2=n+5,~2n-n=5-2,~n=3[/tex]
Explicație pas cu pas:
