问题
解答题
已知数列an的通项公式为an=
|
答案
∵an=n+1 2
∴
=1 anan+2
=2(4 (n+1)(n+3)
-1 n+1
)1 n+3
∴Tn=2(
-1 2
+1 4
-1 3
+…+1 5
-1 n+1
)1 n+3
=2(
+1 2
-1 3
- 1 n+2
)=1 n+3 5n2+25n+24 3(n+2)(n+3)
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