2/(1*4)+2/(4*7)+2/(7*10)+2/(10*13)+...+2/(3n-2)(3n+1)
lim(1/n^2+4/n^2+7/n^2+…+3n-1/n^2)
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
计算1/(m-n)-1/(m+n)-2n/(m^2+n^2)-4n^3/(m^4+n^4)-8n^7/(m^8+n^8)
已知888个连续正整数之和:n+(n+1)+(n+2)+(n+3)+(n+4)+(n+5)+(n+6)+(n+7)+··
4/(1*2*3)+7/(2*3*4)+.+(3n+1)/[n(n+1)(n+2)]
证明:1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+)
M=(N-1)×1+(N-2)×2+(N-3)×4+(N-4)×8+(N-5)×16+(N-6)×32+(N-7)×64
1+4-7+10-……+(-1)^n(3n+2) 求前N项和
[3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简
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