thgtxl888
幼苗
共回答了18个问题采纳率:94.4% 举报
(1)由
1
1×2 =
1
1 -
1
2 ;
1
2×3 =
1
2 -
1
3 ;
1
3×4 =
1
3 -
1
4 ,…则:
1
n(n+1) =
1
n -
1
n+1 ;
(2)
1
n -
1
n+1 =
n+1
n(n+1) -
n
n(n+1) =
n+1-n
n(n+1) =
1
n(n+1) ;
(3)
1
1×2 +
1
2×3 +
1
3×4 +…+
1
2009×2010
=1-
1
2 +
1
2 -
1
3 +
1
3 -
1
4 +…+
1
2009 -
1
2010
=1-
1
2010
=
2009
2010 .
1年前
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