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问题 解答题
已知数列{an}是首项为1，公比为
1
3
的等比数列．
（1）求an的表达式；
（2）如果bn=（2n-1）an，求{bn}的前n项和Sn．
答案

（1）∵{an}是首项为1，公比为

1
3
的等比数列，

∴an=(

1
3
)n-1；

（2）由（1）得，bn=（2n-1）an=（2n-1）(

1
3
)n-1，

∴Sn=1+3×

1
3
+5×(
1
3
)2+…+（2n-1）(
1
3
)n-1①，

1
3
Sn=
1
3
+3×(
1
3
)2+5×(
1
3
)3+(2n-1)•(
1
3
)n②，

①-②得，

2
3
Sn=1+2×
1
3
+2×(
1
3
)2+…+2×(
1
3
)n-1-(2n-1)•(
1
3
)n=1+2×
1
3
[1-(
1
3
)n-1]
1-
1
3
-(2n-1)•(
1
3
)n=2-(
1
3
)n-1-(2n-1)•(
1
3
)n，

∴Sn=3-

n+1
3n-1
．

完形填空
My name is Ann. I am 16 years old. I never try to lose weight (减肥) but I am slim and beautiful.      ? Because I keep a       diet.
     breakfast, I always have some bread and an egg and I drink a glass of milk. It helps me start the day. I usually have breakfast at half past seven.
We have four lessons in the morning. At ten o’clock when I am not studying, I sometimes eat one or two pieces of sugar because I need lots of      .
Lunch usually begins at half past twelve. I often eat       beef, rice and vegetables for lunch. My mum says that lunch is very important so I       miss (错过) lunch at school. One hour after lunch, I eat some   42  . I usually eat one apple or two bananas. I like bananas best.
I drink three or four glasses of       in the afternoon because there is no calories in the water.
For dinner, I often have soup and vegetables. Tomatoes are my favourite. I usually have supper at half past seven. After dinner, I don’t eat or drink       I go to bed.
I never play basketball or volleyball. But I       a lot. I almost go everywhere on foot. That’s why I am so slim.
小题1:
A．WhyB．WhatC．WhereD．When
小题2:
A．deliciousB．smallC．bigD．healthy
小题3:
A．ForB．InC．OnD．To
小题4:
A．moneyB．waterC．foodD．energy
小题5:
A．anyB．someC．littleD．many
小题6:
A．usuallyB．oftenC．sometimesD．never
小题7:
A．breadB．meatC．vegetableD．fruit
小题8:
A．riceB．waterC．CokeD．milk
小题9:
A．whenB．afterC．beforeD．if
小题10:
A．playB．walkC．rideD．drive
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单项选择题

《管理人力资本》一书的作者是（）

A、比尔

B、雷蒙德迈勒斯

C、梅奥

D、怀特巴克
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