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Sn＝213+419+6127+…+(2n+13n)=n(n+1)+1−(13)n2n(n+1)+1−(13)n2．
题目详情
Sn＝2
+4
+6
+…+(2n+
)=
| 1 |
| 3 |
| 1 |
| 9 |
| 1 |
| 27 |
| 1 |
| 3n |
n(n+1)+
1−(
| ||
| 2 |
n(n+1)+
．1−(
| ||
| 2 |
▼优质解答
答案和解析
Sn＝2
+4
+6
+…(2n+
)
=(2+4+6+…+2n)+(
+
+…+
)
=
×n+
=n(n+1)+
故答案为：n(n+′1)+
| 1 |
| 3 |
| 1 |
| 9 |
| 1 |
| 27 |
| 1 |
| 3n |
=(2+4+6+…+2n)+(
| 1 |
| 3 |
| 1 |
| 9 |
| 1 |
| 3n |
=
| 2+2n |
| 2 |
| ||||
1−
|
=n(n+1)+
1−(
| ||
| 2 |
故答案为：n(n+′1)+
1−(
| ||
| 2 |
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