1×3x5+3×5×7+5×7×9+……+17×19×21
来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/05/15 19:21:17
1×3x5+3×5×7+5×7×9+……+17×19×21
显然有:
1×3×5=[1×3×5×7-(-1)×1×3×5]/8,
3×5×7=(3×5×7×9-1×3×5×7)/8,
5×7×9=(5×7×9×11-3×5×7×9)/8,
7×9×11=(7×9×11×13-5×7×9×11)/8,
······
17×19×21=(17×19×21×23-15×17×19×21)/8.
将上述各式相加,得:
1×3×5+3×5×7+5×7×9+7×9×11+······+17×19×21
=[17×19×21×23-(-1)×1×3×5]/8
=[(20+3)(20-3)(20+1)(20-1)+15]/8
=[(400-9)(400-1)+15]/8
=(160000-10×400+9+15)/8
=156024/8
=19503.
1×3×5=[1×3×5×7-(-1)×1×3×5]/8,
3×5×7=(3×5×7×9-1×3×5×7)/8,
5×7×9=(5×7×9×11-3×5×7×9)/8,
7×9×11=(7×9×11×13-5×7×9×11)/8,
······
17×19×21=(17×19×21×23-15×17×19×21)/8.
将上述各式相加,得:
1×3×5+3×5×7+5×7×9+7×9×11+······+17×19×21
=[17×19×21×23-(-1)×1×3×5]/8
=[(20+3)(20-3)(20+1)(20-1)+15]/8
=[(400-9)(400-1)+15]/8
=(160000-10×400+9+15)/8
=156024/8
=19503.
1x5+2x5+3x5+4x5+5x5… 麻烦给我一个公式.
1×3x5+3×5×7+5×7×9+……+17×19×21
(9/5X10/7-3/1)X5/6
宝马的 1 3 5 6 7 x3 x5 x6...
1/1x3+1/3x5+1/5x7+1/7x9+1/9x11=?
X1 - X3 - X4 -5X5=0 X1+2X2+3X3+3X4+7X5=0 X1+X2+X3+X4+X5=0 X2
sn=(2-3x5^-1)+(4-3x5^-2)+…+(2n-3x5^-n)要详解答案,急用!
2/1x3+2/3X5+2/5x7=2/7x9+2/9x11
(7\8-1\5)x5\6=
计算:1/1x3+1/3x5+1/5x7+1/7x9+……+1/2011x2013
3/2 x 5/7 - (-5/7)x5/2 +(-1/2) 除以7/5 等于多少,
1/1X3+1/3X5+1/5X7...1/17X19+1/19X21=