1/1×2×3+1/2×3×4+1/3×4×5+1/4×5×6+.....+1/20×21×22
来源:百度知道 编辑:UC知道 时间:2024/06/08 14:40:35
帮帮我吧,是奥数里的题目,明天要教学生了,非常感谢!
解题思路:
1/(n-1)×n×(n+1)=[1/(n-1)×n-1/n×(n+1)]/2
所以原式=(1/1x2-1/2x3)/2+(1/2x3-1/3x4)/2+(1/3x4-1/4x5)/2+……+(1/20x21-1/21x22)/2
=(1/1x2 -1/2x3+1/2x3 -1/3x4+1/3x4 -1/4x5+……+1/20x21-1/21x22)/2
=(1/1x2-1/21x22)/2
=230/462
=115/231
原式=(1-1/2)*1/3+(1/2-1/3)+1/4......+(1/20-1/21)*1/22
=1/2(1-1/3)-(1/2-1/3)+1/2(1/2-1/4)-(1/3-1/4)......1/2 (1/20-1/22)-(1/21-1/22)
=1/2(1+1/2-1/21-1/22)-(1/2-1/22)
=1/4-1/42+1/44
=3/11-1/42
=115/462
原式=(1/1x2-1/2x3)/2+(1/2x3-1/3x4)/2+(1/3x4-1/4x5)/2+……+(1/20x21-1/21x22)/2
=(1/1x2 -1/2x3+1/2x3 -1/3x4+1/3x4 -1/4x5+……+1/20x21-1/21x22)/2
=(1/1x2-1/21x22)/2
=115/462
1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+100)
1+1/(1+2)+1/(1+2+3)+-------+1/(1+2+3+----+100)
(1/2005-1)(1/2004-1)........(1/3-1)(1/2-1)
1+1/1+2+1/1+2+3+...+1/1+2+3...+2000
1*(1/1+2)*(1/1+2+3)*~~~*(1/1+2+~~~2005)=?
1+1/2+1/3+.....+1/n
1+1/2+1/3+...+1/100
1-1/2+1/3-.....-1/10
(1+1/2+1/3+1/4)×
1/1+2 + 1/1+2+3 +....+ 1/1+2+3+....+100=