（1）ρ = lim a/a= lim (n+1)(n+1)!/[n(n+2)!] = lim (n+1)/[n(n+2)] = 0该级数收敛。∑ n/(n+1)! = ∑ (n+1-1)/(n+1)!= ∑1/n! - ∑1/(n+1)!= (e - 1) - (e - 2) = 1
