问题
填空题
Sn=2
|
答案
Sn=2
+41 3
+61 9
+…(2n+1 27
)1 3n
=(2+4+6+…+2n)+(
+1 3
+…+1 9
)1 3n
=
×n+2+2n 2
(1-1 3
)1 3n 1- 1 3
=n(n+1)+1-(
)n1 3 2
故答案为：n(n+′1)+1-(
)n1 3 2
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Sn=2
|
Sn=2
+41 3
+61 9
+…(2n+1 27
)1 3n
=(2+4+6+…+2n)+(
+1 3
+…+1 9
)1 3n
=
×n+2+2n 2
(1-1 3
)1 3n 1- 1 3
=n(n+1)+1-(
)n1 3 2
故答案为：n(n+′1)+1-(
)n1 3 2