用简便方法计算：1/6+1/12+1/20+1/30+1/42

11 |

原式=1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)
=1/2-1/7
=5/14...

千问 | 2011-6-9 13:08:11 | 显示全部楼层

=1/2-1/3+1/3-1/4....=1/2-1/7=5/14...

千问 | 2011-6-9 13:08:11 | 显示全部楼层

1/6+1/12+1/20+1/30+1/421/4+1/20+1/30+1/423/10+1/30+1/421/3+1/4215/425/14...

千问 | 2011-6-9 13:08:11 | 显示全部楼层

=1/2-1/7=5/14...

千问 | 2011-6-9 13:08:11 | 显示全部楼层

1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)=1/2-1/7=5/14...

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