1+(-2)+3+(-4)+...+(-1)n+1 n.

证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 化简：1/(n+1)(n+2)+1/(n+2)(n+3)+1/(n+3)(n+4) (n+1)(n+2)/1 +(n+2)(n+3)/1 +(n+3)(n+4)/1 证明：1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+) [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 化简(n+1)(n+2)(n+3) 2^n/n*(n+1) 若n为正整数,求1/n(n+1)+1/(n+1)(n+2)＋1/(n+2)(n+3)+1/(n+3)(n+4)+.+1/ 用数学归纳法证明：1×2×3+2×3×4+…+n×(n+1)×(n+2)＝n(n+1)(n+2)(n+3)4(n∈N lim(1/n^2+4/n^2+7/n^2+…+3n-1/n^2) 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)]