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公务员数学运算题一道

来源:学生作业帮 编辑:拍题作业网作业帮 分类:数学作业 时间:2024/04/29 22:51:57
公务员数学运算题一道
D.11/45
1/(1×2×3)=[1/(1×2)-1/(2×3)]/2
1/(2×3×4)=[1/(2×3)-1/(2×3)]/2
1/(3×4×5)=[1/(3×4)-1/(4×5)]/2
1/(4×5×6)=[1/(4×5)-1/(5×6)]/2
.
1/(8×9×10)=[1/(8×9)-1/(9×10)]/2
所以
1/(1×2×3)+1/(2×3×4)+…+1/(8×9×10)
=[1/(1×2)-1/(2×3)]/2+[1/(2×3)-1/(2×3)]/2+[1/(3×4)-1/(4×5)]/2+[1/(4×5)-1/(5×6)]/2+...+[1/(8×9)-1/(9×10)]/2
=[1/(1×2)-1/(2×3)+1/(2×3)-1/(2×3)+1/(2×3)-1/(2×3)+1/(3×4)-1/(4×5)+1/(4×5)-1/(5×6)+...+1/(8×9)-1/(9×10)]/2
=[1/(1×2)-1/(9×10)]/2
=(1/2-1/90)/2
=(44/90)/2
=22/90
=11/45