求1+3+5+7+9+11+13+.+（2n-1)+(2n+1)

1\n(n+3)+1\(n+3)(n+6)+1\(n+6)(n+9)=1\2 n+18 n为正整数,求n的值 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 若3n^2-n=1,求6n^3+7n^2-5n+2003的值 求1+3+5+7+9+11+13+.+（2n-1)+(2n+1) lim 9^n+4^n+2/5^n-3^2n-1 n趋于无穷大时 ∑（N等于1,2,3,4..n） 5^N/N!,极限怎么求 (5^n+(-2)^n)/(5^(n+1)+(-2)^(n+1))当n趋近无穷,求极限. 求极限lim [ 2^(n+1)+3^(n+1)]/2^n+3^n (n→∞) 求极限 n趋向无穷 2^n+1 + 3^n+1/2^n+3^n 若n²+3n=1,求n(n+1)(n+2)+1的值. 求lim(n+1)(n+2)(n+3)/(n^4+n^2+1) 求极限 lim(n->无穷)[(3n^2-2)/(3n^2+4)]^[n(n+1)]