问题
填空题
若Sn=
|
答案
因为
=1 n2+2n
(1 2
-1 n
)，1 n+2
所以Sn=
+1 12+2
+1 22+4
+…+1 32+6 1 n2+2n
=
(1 2
-1 1
+1 3
-1 2
+1 4
-1 3
+…+1 5
-1 n
)1 n+2
=
(1+1 2
-1 2
-1 n+1
)．1 n+2
所以
Sn=lim n→∞ lim n→∞
(1+1 2
-1 2
-1 n+1
)=1 n+2
(1+1 2
)=1 2
．3 4
故答案为：
．3 4