1-2+3-4+5-6+…+2n-1-2n=?

1+(n+2)+(2n+3)+(3n+4)+(4n+5)+……((n-1)n+n)的答案 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+(n+1)+(n+2)+(n+3)+(n+4)=5n+10这道题怎么解 lim(1/n+2/n+3/n+4/n+5/n+……+n/n)=lim(1/n)+lim(2/n)+……+lim(n/n)成立吗?（n趋近于无穷大）为什么不成立? 下列几组力中,合力不可能等于0的是 A.3N 4N 6N B.1N 2N 4N C.2N 4N 6N D.5N 5N 1N 1/[n(n+1)]+1/[(n+1)(n+2)]+1/[(n+2)(n+3)]+1/[(n+3)(n+4)]+[(n+4)(n+5)}怎么算谢谢了, [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 [3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 1*3*4+2*6*8+………+n*3n*4n / 1*4*5+2*8*10+………+n*4n*5n 计算(1×2×3+2×4×6+…+n×2n×3n)÷(1×3×5+2×6×10+…+n×3n×5n) 根号（1×2×3+2×4×6+…+n×2n×3n)÷根号（1×5××10+2×10×20+…+n×5n×10n)=? 根号（1×2×3+2×4×6+…+n×2n×3n)÷根号（1×5××10+2×10×20+…+n×5n×10n)=? 1+2+3+4+……+n=n(n+1)(2n+1)/6 lim(1/n^2+4/n^2+7/n^2+…+3n-1/n^2) 求证：N=(5^2)*(3^2n+1)*(2^n)-(3^n)*(6^n+2) 请解(n+1)/2n之和( n=1,2,3,4,5…n) ∑(∞,n=1)(n^2-2n+3)/(n^4+n^2-6)