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问题 解答题
.在等比数列{an}中，an＞0（n∈N*），公比q∈（0，1），且a1a5+2a3a5+a2a8=25，又2是a3与a5的等比中项．设bn=5-log2an．
（1）求数列{bn}的通项公式；
（2）已知数列{bn}的前n项和为Sn，Tn=
1
S1
+
1
S2
+…+
1
Sn
，求Tn．
答案

（1）∵a1a5+2a3a5+a2a8=25，∴a32+2a3a5+a52=25，又an＞0，∴a3+a5=5，

又2为a3与a5的等比中项，∴a3a5=4．

而q∈（0，1），∴a3＞a5，∴a3=4，a5=1，∴q=

1
2
，a1=16，

∴通项公式 an=16×(

1
2
)n-1=25-n，bn=5-log2an=5-（5-n）=n，∴Sn=
n(n+1)
2
．

（2）

1
S
n=
2
n(n+1)
=2(
1
n
-
1
n+1
)，

∴Tn=

1
S1
+
1
S2
+…+
1
Sn
=2[(1-
1
2
)+(
1
2
-
1
3
)+…+(
1
n
-
1
n+1
)]=2(1-
1
n+1
)=
2n
n+1
．

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A.胸膜腔闭式引流

B.抗休克

C.可用一粗针头在锁骨中线第二肋间插入

D.应用抗生素

E.吸氧

F.应用洋地黄制剂
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阅读理解

The crisis at Japan’s Fukushima Daiichi nuclear energy center caused by the terrible earthquake has raised questions about the future of the nuclear energy industry. Arjun is president of the Institute for Energy and Environmental Research in the United States. He says the disaster in Japan is historic.

This week, the chairman of America’s nuclear agency said there is little chance that harmful radiation(辐射) from Japan could reach the United States. Gregory also said America has a strong program in place to deal with earthquake threats. No new nuclear power centers have been built in the United States since 1979. That was when America’s worst nuclear accident happened at the Three Mile Island center in Pennsylvania. The accident began to turn public opinion against nuclear energy. At present, about twenty percent of electricity in the United States comes from nuclear energy.

German Chancellor Angela Merkel said Germany would close seven nuclear power centers for the time being while energy policy is reconsidered. The European Union is planning to test all centers in its twenty-seven member nations.

Developing nations are less willing to slow down the development of nuclear. China says it will continue with plans to build about twenty-five new nuclear reactors(核反应堆). And India, under a cooperation agreement with the United States, plans to spend billions on new centers in the coming years.

Nuclear reactors supply fourteen percent of global electricity. Nuclear energy is a clean resource, producing no carbon gases. But radioactive waste is a serious problem to be solved. So is the presence of nuclear power centers in earthquake areas like the one near Bushehr, lran.

小题1:We can learn from the text that America ________.

A．experienced a terrible nuclear accident 32 years ago

B．has a strong program to deal with radiation danger

C．depends heavily on nuclear energy to produce electricity

D．will check all the reactors before cooperating with India小题2:According to the text, which country will be most likely to have a similar disaster?

A．German.

B．Iran

C．India.

D．China.小题3:How does the author seem to feel about the future of nuclear energy?

A．Satisfied.

B．Pleased.

C．Worried.

D．Surprised.小题4:The best title of the text is ______.

A．Various Opinions on Japan’s Nuclear Disaster

B．Japan’s Disaster is Likely to Run Out of Control

C．America Shows Great Concern for Japan’s Nuclear Crisis

D．Japan’s Disaster Throws Doubt on Nuclear Energy Industry
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