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问题 填空题

等差数列{an}的前n项和为Sn ，已知S10=0，S15 =25，则nSn 的最小值为________.

答案

由题意知：，解得，，所以

=，即nSn =，令，则有，令得，，令得，，又因为n为正整数，所以当时，所以取得最小值，即nSn 的最小值为.

【考点定位】本小题主要考查等差数列的前n项和公式的应用、导数求数列这一特殊函数的最值，要注意n取正整数这一条件，考查同学们分析问题、解决问题的能力.

选择题

台湾省的行政中心是：[ ]

A．高雄

B．台北

C．台中

D．福州
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阅读理解
阅读理解。
                                                                                                              237 West Palmdale Boulevard
                                                                                                              Fresno, Califormia93706
AmToy Corporation
Suite 15
TransAm Building
November 20, 2008
Dear Sirs,
     As a concerned parent, I am writing to protest your recent advertisement for Electro-Rain seen in local
media is California. Specially, I am referring to newspaper and magazine ads (attached this letter) and had
the week of November 15.
     Children respond to your type of advertising in an immature way; that is, they are able to understand
how expensive some toys are for middle-class parent. Further, your product is violent in nature. Youth
advertisement gives children the impression that it's fine to have "two guns and laser eyes." You also
suggest that children need your toy protect them "when you go outside." This is not a healthy attitude for
children to have.
     I hope you will stop advertising your product in such a way that may our children. 
                                                                                                                Sincerely yours,
                                                                                                               (Mrs.) Alma Hernandez Enc
     It's here! Ready for You, Now! It's Electro-Robo!
     Every lay dreams of being in control of a robot, and AmToy can make your dream come true Electro-
R0ho is the world's first fully autocratic robot with radio control. Standing 80 centimeters tall, Electro-Robo
is like a friend at home. He can walk, talk, and even shake your had! He has two guns and laser eyes to help
you defend yourself when you go outside with him. Every boy needs Electro-Robo!
     Ask your Mom and Dad to buy Electro-Robo for your birthday or for Christmas, which is coming up
soon. Imagine that you are in control of your friend for life, Electro-Robo!
     Available at all toy stores and department stores NOW!
1. What is the purpose of the letter?
A. To complain about a broken toy.
B. To oppose the advertising.
C. To order a gift for Chrisman.
D. To apply for a job in a toy company.
2. Why does the writer of the letter that Electro-Robo is violent?
A. It is controlled by radio water.
B. It is expensive to buy.
C. It is 80 centimeter.
D. It bears arms.
3. What dose "End" at the end of the letter mean?
A. Something attached to the letter.
B. A complaint to the toy company.
C. A hidden message.
D. An encouraging response.
4. Electro-Robo can do all the following EXCEPT _____. 
A. sitting down
B. shaking hands
C. talking
D. walking
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