limn→∞ n((2n+1)2)(n+2)(n2+3n−1) =
0
2
4
∞
limn→∞ n(2n+1)2(n+2)(n2+3n−1) = limn→∞(4n3+4n2+n)(n3+5n2+5n−2) =limn→∞ n3×(4+4n+1n2)n3(1+5n+5n2−2n3) =4