若1/1×2+1/2×3+1/3×4……+1/（n-1)n=25/26则n= ______

证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 求极限Xn=n/(n^2+1)+n/(n^2+2)+n/(n^2+3)+……+n/(n^2+n), (1/(n^2 n 1 ) 2/(n^2 n 2) 3/(n^2 n 3) ……n/(n^2 n n)) 当N越于无穷大 1 + (n + 1) + n*(n + 1) + n*n + (n + 1) + 1 = 2n^2 + 3n + 3 证明：1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+) 证明(1+2/n)^n>5-2/n（n属于N+,n>=3) 用数学归纳法证明：（n+1）+（n+2）+…+（n+n）=n(3n+1)2 已知n∈N+,则1+3C(n,1)+3^2C(n,2)+…+3^nC(n,n)等于______ lim 1+4+7+...+(3n-2)/n(n+1)=______ f(n)=1/(n+1)+1/(n+2)+1/(n+3)……+1/2n (n∈N*),f(n+1 数学归纳法证明：1*n+2(n-1)+3(n-2)+…+(n-1)*2+n*1=(1/6)n(n+1)(n+2) 用数学归纳法证明：1*n+2(n-1)+3(n-2)+…+(n-1)*2+n*1=(1/6)n(n+1)(n+2)