x_n = (n^2)^(-1/2) + (n^2+1)^(-1/2) + (n^2+2)^(-1/2) + ...+
x_n = (n^2)^(-1/2) + (n^2+1)^(-1/2) + (n^2+2)^(-1/2) + ...+
递归证明一题x0=0,x1=1,x_(n+1)=4x_n -3x_(n-1)求证 x_n=(3^n-1)/2
2^n/n*(n+1)
证明不等式:(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n
阶乘(2n-1)!=(2n)!/(2^n*n!
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?
1 + (n + 1) + n*(n + 1) + n*n + (n + 1) + 1 = 2n^2 + 3n + 3
[3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简
证明(1+2/n)^n>5-2/n(n属于N+,n>=3)
化简(n+1)(n+2)(n+3)
n(n+1)(n+2)数列求和
n(n+1)(n+2)等于多少?