1/6+1/12+1/20…+1/n(n+1)=
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1/6+1/12+1/20…+1/n(n+1)=1/6+1/12+1/20…+1/n(n+1)=1/6+1/12+1/20…+1/n(n+1)=1/6+1/12+1/20…+1/n(n+1)==1/2
1/6+1/12+1/20…+1/n(n+1)=
1/6+1/12+1/20…+1/n(n+1)=
1/6+1/12+1/20…+1/n(n+1)=
1/6+1/12+1/20…+1/n(n+1)=
=1/2×3＋1/3×4＋1/4×5＋...+1/n(n+1)
=1/2-1/3+1/3-1/4+1/4-1/5+...+1/n-1/(n+1)
=1/2-1/(n+1)
=(n-1)/[2(n+1)]
[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
n^(n+1/n)/(n+1/n)^n
2^n/n*(n+1)
计算2+6+12+20+……+(n-1)n
(n+1)^n-(n-1)^n=?
化简：(n+1)!/n!-n!/(n-1)!
(n-1)*n!+(n-1)!*n
推导 n*n!=(n+1)!-n!
证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n
1/2+5/6+11/12+19/20+29/30+……+n平方-n-1/n(n-1)
用数学归纳法证明 6+2*9+3*12+…+n(3n+3)=n(n+1)(n+2)
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?
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)
根号（n+1)+n
n.(n-1).
(n+2)!/(n+1)!
判断 当n>1时,n*n*n>3n.( )