问题
解答题
求数列
|
答案
∵
=1 n(n+2)
(1 2
-1 n
）1 n+2
∴Sn=
[(1-1 2
)+(1 3
-1 2
)+…+(1 4
-1 n
)]1 n+2
=
(1-1 2
-1 2
-1 n+1
)1 n+2
=
-3 4
-1 2n+2 1 2n+4
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求数列
|
∵
=1 n(n+2)
(1 2
-1 n
）1 n+2
∴Sn=
[(1-1 2
)+(1 3
-1 2
)+…+(1 4
-1 n
)]1 n+2
=
(1-1 2
-1 2
-1 n+1
)1 n+2
=
-3 4
-1 2n+2 1 2n+4