vigerking
幼苗
共回答了17个问题采纳率:88.2% 举报
1
2 +
5
6 +
11
12 +
19
20 +…+
379
380 ,
=(1-
1
2 )+(1-
1
6 )+(1-
1
12 )+(1-
1
20 )+…+(1-
1
380 ),
=19-(
1
2 +
1
6 +
1
12 +
1
20 +…+
1
380 ),
=19-(1-
1
2 +
1
2 -
1
3 +
1
3 -
1
4 +…+
1
19 -
1
20 ),
=19-1+
1
20 ,
=18
1
20 .
故答案为:18
1
20 .
1年前
1