an=1+6×(1+2+...+n-1)=1+6×(n-1)n/2=3n(n-1)+1=3n²-3n+1
证明不等式:(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n
1 + (n + 1) + n*(n + 1) + n*n + (n + 1) + 1 = 2n^2 + 3n + 3
证明(1+2/n)^n>5-2/n(n属于N+,n>=3)
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
[3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简
Sn=n(n+2)(n+4)的分项等于1/6[n(n+2)(n+4)(n+5)-(n-1)n(n+2)(n+4)]吗?
(n+1)^n-(n-1)^n=?
若n²+3n=1,求n(n+1)(n+2)+1的值.
3n²-n=1 求6n³+7n²-5n+2014
求数列an=n(n+1) 的前n项和 到 an=n(n+1)=[n(n+1)(n+2)-(n-1)n(n+1)]/3(裂
证明:1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+)
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)