1-1/2-1/6-1/12-1/30
=1-[1/2+1/2-1/3+1/3-1/4+1/30]
=1-(1-1/4+1/30)
=1-1+1/4-1/30
=1/4-1/30
=13/30
。。。。。。。。。。。。。。。。。。。。。
1-1/2-1/6-1/12-1/20-1/30
=1-[1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6]
=1-(1-1/6)
=1-1+1/6
=1/6
我怎么觉得少了一个1/20
1-1/2-1/6-1/12-1/20-1/30
=1-(1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)
=1/6
中间上不是还缺了一个1/20?
1-1/2-1/6-1/12-1/30
=1-(1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/5-1/6)
13/60