-
新人教版高中英语必修2Unit 2 Wildlife Protection-Reading and Thinking教案一
The listening and speaking part aims at how to protect and help endangered animals by listening, speaking and talking about the facts and reasons. This lesson analyzes the decreasing clause of Tibetan antelope population and the measures of protecting Tibetan antelopes. So students can be guided to learn to analyse the title and use different reading skills or strategies, like scanning, skimming and careful reading.1. Read quickly to get the main ideas and the purpose of going to Tibetan; read carefully to understand what the author see and think.2. Understand the sentences of the present continuous passive voice such as “Much is being done to protect wildlife.” and the inverted sentence “Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.”3. Enhance the awareness of protecting wildlife.4. Cultivate the reading methods according to different materials.1. Read quickly to get the main ideas and the purpose of going to Tibetan; read carefully to understand what the author see and think.2. Understand the sentences of the present continuous passive voice such as “Much is being done to protect wildlife.” and the inverted sentence “Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.”3. Cultivate the reading methods according to different materials.Step 1 Leading-inWatch a video about elephants and whales and then ask:Why are they endangered ? They are killed/hunted
新人教版高中英语必修2Unit 2 Wildlife Protection-Reading For Writing教案一
1. 标题首先根据海报的特点、格式写明标题。海报中往往把内容作为大标题。例如: Save the earth, Save the birds。2. 正文部分不同的海报其正文部分的侧重点不同。对于介绍性的海报, 首先要引出话题, 其次列出原因, 最后是总结。对于宣传类的海报, 要写明具体内容, 如: 活动内容, 地点以及参加活动的注意事项, 主持或举办单位等。1. 图片: 要选择引人注目的图片, 与主题要相关, 色彩明亮。话题句式 1. It is a treasure of our country. 它是我国的国宝。2. Believe it or not, at present only several thousand pandas exist in the world. 信不信由你, 目前世界上仅现存几千只熊猫。 3.It’s because of human activities that tigers are endangered. 正是因为人类的活动, 老虎处于濒危的状态。4. Many wild animals are in danger of dying out. 很多野生动物面临着灭绝的危险。 5. The government has taken effective measures to protect them. 政府已采取有效的措施来保护它们。6. People should raise the awareness of the protection of wild animals. 人们应该提高保护野生动物的意识。 7. It’s amazing that there are merely less than 1, 000 finless porpoises living in China. 非常令人吃惊, 目前中国仅有不足1 000只江豚。
新人教版高中英语必修2Unit 3 The Internet-Discovering Useful Structure教案一
This unit is about the Internet, which has a great influence to our humans and our lives. During the Listening & Speaking & Talking and Reading and Thinking section, the influence in examples has been shown. Thus, use the Present Perfect Tense is appropriate. However, in order to show the justice or weaken the doer of the behavior/action, it’s better to use the Present Perfect Passive Voice than the Present Perfect Tense. Besides, having learned to use the Present Perfect Passive Voice, students can beautify their language in their writing. 1. Learn the structure of the Present Perfect Passive Voice and its functions. 2. Learn to change the sentences with the Present Perfect Passive Voice into the sentences with the Present Perfect Passive Voice. 3. Learn to write sentences with the Present Perfect Passive Voice flexibly according to the context. 1. Learn the structure of the Present Perfect Passive Voice and its functions. 2. Learn to change the sentences with the Present Perfect Passive Voice into the sentences with the Present Perfect Passive Voice. 3. Learn to write sentences with the Present Perfect Passive Voice flexibly according to the context. Step 1 Observe the following sentences, then change the sentences into passive voice.He has been selected to take part in the sports meeting．(肯定句)他已被挑选出来参加运动会。The ink has not been removed from his overcoat．(否定句)墨迹还没有从他外套上去掉。
新人教版高中英语必修2Unit 3 The Internet-Listening &Speaking＆Talking教案一
Listening and Speaking introduces the topic of “ask about online habits”. Many middle school students have been surfing the Internet for many years, but what they do with the Internet and how much time they spend every day may not be very clear to themselves, nor to other students. This section allows students to investigate their peers' Internet use, which is conducive to their mutual understanding and understanding of the Internet. It can also help them reflect on their own online behavior, learn from other people's good online habits, and get rid of their bad online behavior.The listening text of this section is an investigation interview. The investigators interview specific groups with the same questions to obtain information, so as to understand their views, practices or attitudes on this issue. There are two specific questions: “how much time do you spend online every day? What do you usually do online?”. The answers of the three respondents provide rich and different information, and achieve the purpose of the investigators. The oral discourse structure of survey interviews generally includes greeting and explaining the purpose of the interview, presenting the interview questions and the respondents' answers. Listening and Talking introduces the theme of “choosing the right application ". Listening text is a conversation between Laura and Xiao Bo. In this part of listening, “oink”； “piggy bank” may cause the students' hearing comprehension limitation. Oink refers to sound word and pig's sound. So, add some oink to my piggy bank is often used to describe "making a little money".1. Guide students to understand the content of listening texts in terms of listening for definitions.2. Cultivate students' ability to define words and understand an investigation interview.
新人教版高中英语必修2Unit 4 History and Traditions-Discovering Useful Structure教案一
Step 5 Practice一、完成下列句子。1. Judy and I _______________（把车停下来(park)）in an underground car Park near Trafalgar Square, where we could ______________________(让我们的车充电（charge)).2. When we finally reached the service desk to ask for audio guides, we heard it ___________ that there were no audio guides____________(留下，剩下）.3. We__________________________（发现自己对...很惊讶）the large number of visitors and the amount of noise at the entrance of the National Gallery.4. Judy ____________________(眼神专注于） Van Gogh’s Sunflowers. It was hard to approach the painting as there were so many people around.5. She ____________________(把这幅画的复制品装箱（box)） to ensure that it was delivered safely.答案：1.had our car parked get our car battery charged 2. announced left 3. found ourselves very surprised 4. had her eyes fixed on 5. had a copy of the painting boxed二、用过去分词对下列句子进行改写。1. Loch Ness was surrounded by beautiful natural landscape, which made it look amazing.2. Carl and his friend stayed with a generous family who offered them bread with butter and honey that was homemade.3. The family’s ancestors once attended to soldiers who were wounded in the First World War.4. The young people were attracted by the legend of Loch Ness. They watched over the lake with their cameras and binoculars, which were positioned on the hill.答案：1. Loch Ness surrounded by beautiful natural landscape looks amazing.2. Carl and his friends stayed with a generous family who offered them homemade bread with butter and honey.3. The family’s ancestors once attended to wounded soldiers in the First World War.4. The young people attracted by the legend of Loch Ness watched over the lake with their cameras and binoculars positioned on the hill.
新人教版高中英语必修2Unit 4 History and Traditions-Listening＆Speaking＆Talking教案一
This unit is about history and traditions. From the opening page, we can know that this unit will introduce the history and traditions around the world. As Marcus Garvey says “A people without the knowledge of their past history, origin and culture is like a tree without roots”, it is important for students to realize the importance and value of knowing the history and traditions and their further meanings. And this part ( listening and speaking ) is divided into two parts: Part A---share views on historic sites, Part B ---talk about a visit to a historic tourist destination. By talking with a foreigner, the speakers introduce the historic attractions and their cultures. Part A is that William, a British student, who was going to visit the Confucius Temple and a Chinese student, Xiao Kong, who was going to the Confucius Temple to meet with the members of the research group, went together and exchanged their views on the Confucius Temple, Confucius, Confucius' descendants and Confucius' educational thoughts. Part B is a conversation between Xiao Yan, a youth hostel receptionist and Paul, a backpacker about the feelings and experience after visiting the Chinese famous tourist attraction Pingyao.1. Guide students to understand the content of listening texts in terms of the whole and key details; 2. Cultivate students' ability to guess the meaning of words in listening; discuss with their peers how to talk about historic spots and great person.3. Instruct students to use functional sentences of showing one’s excitement, surprise and disappointment.1. Guide students to understand the content of listening texts in terms of the whole and key details; 2. Cultivate students' ability to discuss with their peers the related topics.3. Enable students to use the functional items of showing one’s excitement, surprise and disappointment.
新人教版高中英语必修2Unit 3 The Internet-Reading For Writing教案一
⑦identity theft 身份盗窃⑧chat room 聊天室⑨draft your blog post 起草博客帖子⑩post embarrassing photos 张贴尴尬照片 【话题句式】 1. How do you stay safe online and avoid bad experiences on the Internet? 你如何在网上保持安全, 避免在网上的不良经历? 2. I’m not an expert, but many years as a blogger have taught me a thing or two. 我不是专家, 但作为一个博主, 我已经学了好几年了。 3. If you see or read something that makes you feel uncomfortable, leave the site immediately. 如果你看到或读到一些让你觉得不舒服的东西, 立即离开这个网站。4. Don’t give out your address or phone number. 别告诉别人你的地址或电话号码。 5. Identity theft is a common and serious problem. 身份盗窃是一个常见而严重的问题。6. Being online is no excuse for being rude, and you don’t want to become a target for a troll or cyberbully. 上网并不是无礼的借口, 你也不想成为发挑衅帖子的人或网络恶霸的目标。 7. Trolls often use several false names so that they can stay on a site. 发挑衅帖子的人经常使用几个假名, 这样他们就可以留在一个网站上。8. However, the more polite you are, the less likely it is you will be attacked. 然而, 你越有礼貌, 你被攻击的可能性就越小。
新人教版高中英语必修2Unit 4 History and Traditions-Reading and Thinking教案一
Features of languages1．Finally, in the 20th century, the southern part of Ireland broke away from the UK, which resulted in the full name we have today: the United Kingdom of Great Britain and Northern Ireland．该句是一个复合句。该句主句为：the southern part of Ireland broke away from the UK；which resulted in the full name we have today为which引导的定语从句代指前面整句话的内容，we have today为定语从句修饰先行词name。译文：最后，在20世纪，爱尔兰南部脱离英国，这导致了我们今天有的英国的全名：大不列颠及北爱尔兰联合王国。2．Almost everywhere you go in the UK, you will be surrounded by evidence of four different groups of people who took over at different times throughout history．该句是一个复合句。该句主句为：you will be surrounded by evidence of four different groups of people；其中Almost everywhere you go in the UK为让步状语从句； who took over at different times throughout history为定语从句修饰先行词people。译文：几乎无论你走到英国的任何地方，你都会发现历史上有四种不同的人在不同的时期统治过英国。3．The capital city London is a great place to start, as it is an ancient port city that has a history dating all the way back to Roman times．该句是一个复合句。该句主句为：The capital city London is a great place to start; as it is an ancient port city that has a history dating all the way back to Roman times．为原因状语从句；dating all the way back to Roman times为现在分词短语作定语修饰history。
新人教版高中英语必修2Unit 5 Music-Discovering Useful Structures教案一
Step1:自主探究。1．(教材P52)Born(bear) in the USA on 2 January 1970, Whitacre began studying music at the University of Nevada in 1988．2．(教材P52) Moved(move) by this music, he said, “It was like seeing color for the first time．”3．(教材P56)I was very afraid and I felt so alone and discouraged(discourage)．4．(教材P58)Encouraged(encourage) by this first performance and the positive reaction of the audience, I have continued to play the piano and enjoy it more every day．Step2:语法要点精析。用法1：过去分词作表语1）．过去分词可放在连系动词be, get, feel, remain, seem, look, become等之后作表语，表示主语所处的状态Tom was astonished to see a snake moving across the floor．汤姆很惊讶地看到一条蛇正爬过地板。Finally the baby felt tired of playing with those toys．终于婴儿厌倦了玩那些玩具。注意：1）.过去分词作表语时与被动语态的区别过去分词作表语时，强调主语所处的状态；而动词的被动语态表示主语是动作的承受者，强调动作。The library is now closed．(状态)图书馆现在关闭了。The cup was broken by my little sister yesterday．(动作)昨天我妹妹把杯子打碎了。2）感觉类及物动词的现在分词与过去分词作表语的区别过去分词作表语多表示人自身的感受或事物自身的状态，常译作“感到……的”；现在分词多表示事物具有的特性，常译作“令人……的”。
新人教版高中英语必修2Unit 5 Music-Reading and Thinking教案一
This section focuses on "learning about experiencing music Online". This virtual choir is a new form of music performance. Members from all over the world don't need to love to come to a place. Instead, they use the new technology to model the various parts and wonderful virtual harmony group of music in the family. Students need to understand the main meaning of each paragraph. Finding topic sentences is an important way to understand the general idea of a paragraph. After the topic sentence, it is usually the detail sentence that supports and explains the topic sentence. Some paragraphs have obvious subject sentences, for example, the first sentence of the second paragraph is the subject sentence of the paragraph, and the following sentenceStudents need to pay attention to the topic sentences and key sentences, and then pay attention to how the sentences after the meaning explain, explain and support the topic sentences or key sentences before.1.Guide students to learn about experiencing music online2.Guide students to scan and circle the information in the text.3.Guide students to find the numbers and dates to fill in the timeline.4.Guide students to learn more about music by completing the sentences with the correct forms of the words and phrases. And then make a mind map about the outline of the passage.1. Guide students to pay attention to reading strategies, such as prediction, self-questioning and scanning.2. Help students sort out the main meaning of each paragraph and understand the narrative characteristics of "timeline” in illustrative style.3. Lead students to understand the changes that have been caused by the Internet.
新人教版高中英语必修2Unit 5 Music-Reading For Writing教案一
(4)Now we have heard a number of outstanding speeches ... 我们已经聆听了许多精彩的发言……(5)Because we wanted the nations of the world, working together, to deal with ... 因为我们希望全世界各国团结起来去应对……(6)And if we do not act ... 如果我们不采取行动……(7)Now, I share the concerns that have been expressed ... 我也同意对于……表达的担心(8)Let us show the world that by working together we can ... 让我们告诉全世界，通过一起努力我们可以……(9)It is now time for us to ... 是时候我们……(10)And I have always wished that ... 我一直希望……(11)Thank you for letting me share this day with me.感谢你们和我共度这一天。实践演练：假如你是高中生李华，你校将举办一次以“音乐”为主题的演讲比赛，请你按照主题，写下你的演讲稿。注意：词数100左右。First of all, thank you for listening to my speech. My topic is: love music like love yourself.Music is like the air we need to maintain our normal lives around us. You can't imagine how terrible a world without music would be. Movies and TV shows have no music, only dry conversations and scenes; mobile phones only vibrations; streets only noisy crowds; cafes, western restaurants only depressed meals. What a terrible world it is!As a student, I hope we all can enjoy the fun brought by music in our spare time. Instead of just listening to music, we can even make our own music. Let's enjoy the fun of music!Thanks again for your attention!
【高教版】中职数学拓展模块：1.2《正弦型函数》教学设计
教 学 过 程教师 行为学生 行为教学 意图时间 *揭示课题 1.2正弦型函数． *创设情境 兴趣导入 与正弦函数图像的做法类似，可以用“五点法”作出正弦型函数的图像．正弦型函数的图像叫做正弦型曲线． 介绍 播放 课件 质疑 了解 观看 课件 思考 学生自然的走向知识点 0 5*巩固知识 典型例题 例3 作出函数在一个周期内的简图． 分析 函数与函数的周期都是，最大值都是2，最小值都是－2. 解 为求出图像上五个关键点的横坐标，分别令，，，，，求出对应的值与函数的值，列表1-1如下： 表 001000200 以表中每组的值为坐标，描出对应五个关键点（，0）、（，2）、（，0）、（，?2）、（，0）．用光滑的曲线联结各点，得到函数在一个周期内的图像（如图）． 图 引领 讲解 说明 引领 观察 思考 主动 求解 观察 通过 例题 进一 步领 会 注意 观察 学生 是否 理解 知识 点 15
人教版高中数学选择性必修二等差数列的前n项和公式（1）教学设计
高斯（Gauss，1777－1855），德国数学家，近代数学的奠基者之一. 他在天文学、大地测量学、磁学、光学等领域都做出过杰出贡献. 问题1：为什么1＋100＝2＋99＝…＝50＋51呢？这是巧合吗？试从数列角度给出解释.高斯的算法：（1+100）+（2+99）+…+(50+51)= 101×50=5050高斯的算法实际上解决了求等差数列：1，2，3，…，n，"… " 前100项的和问题.等差数列中，下标和相等的两项和相等.设 an＝n，则 a1＝1，a2＝2，a3＝3，…如果数列{an} 是等差数列，p，q，s，t∈N*，且 p＋q＝s＋t，则 ap＋aq＝as＋at 可得：a_1+a_100=a_2+a_99=?=a_50+a_51问题2： 你能用上述方法计算1＋2＋3＋… ＋101吗？问题3： 你能计算1＋2＋3＋… ＋n吗？需要对项数的奇偶进行分类讨论.当n为偶数时， S_n=(1+n)+[(2+(n-1)]+?+[(n/2+(n/2-1)]=(1+n)+(1+n)…+(1+n)=n/2 (1+n) =(n(1+n))/2当n为奇数数时， n－1为偶数
人教版高中数学选择性必修二导数的四则运算法则教学设计
求函数的导数的策略(1)先区分函数的运算特点，即函数的和、差、积、商，再根据导数的运算法则求导数；(2)对于三个以上函数的积、商的导数，依次转化为“两个”函数的积、商的导数计算．跟踪训练1 求下列函数的导数：(1)y＝x2＋log3x； (2)y＝x3·ex； (3)y＝cos xx.[解] (1)y′＝(x2＋log3x)′＝(x2)′＋(log3x)′＝2x＋1xln 3.(2)y′＝(x3·ex)′＝(x3)′·ex＋x3·(ex)′＝3x2·ex＋x3·ex＝ex(x3＋3x2)．(3)y′＝cos xx′＝?cos x?′·x－cos x·?x?′x2＝－x·sin x－cos xx2＝－xsin x＋cos xx2.跟踪训练2 求下列函数的导数（1）y＝tan x； （2）y＝2sin x2cos x2解析：（1）y＝tan x＝sin xcos x，故y′＝?sin x?′cos x－?cos x?′sin x?cos x?2＝cos2x＋sin2xcos2x＝1cos2x.（2）y＝2sin x2cos x2＝sin x，故y′＝cos x.例5 日常生活中的饮用水通常是经过净化的，随着水的纯净度的提高，所需进化费用不断增加，已知将1t水进化到纯净度为x%所需费用（单位：元），为c(x)=5284/(100-x) (80<x<100)求进化到下列纯净度时，所需进化费用的瞬时变化率：（1） 90% ；（2） 98%解：净化费用的瞬时变化率就是净化费用函数的导数；c^' (x)=〖(5284/(100-x))〗^'=(5284^’×(100-x)-"5284 " 〖(100-x)〗^’)/〖(100-x)〗^2 =(0×(100-x)-"5284 " ×(-1))/〖(100-x)〗^2 ="5284 " /〖(100-x)〗^2
人教版高中数学选修3成对数据的相关关系教学设计
由样本相关系数??≈0.97,可以推断脂肪含量和年龄这两个变量正线性相关，且相关程度很强。脂肪含量与年龄变化趋势相同.归纳总结1．线性相关系数是从数值上来判断变量间的线性相关程度，是定量的方法．与散点图相比较，线性相关系数要精细得多，需要注意的是线性相关系数r的绝对值小，只是说明线性相关程度低，但不一定不相关，可能是非线性相关．2．利用相关系数r来检验线性相关显著性水平时，通常与0.75作比较，若|r|>0.75，则线性相关较为显著，否则不显著．例2. 有人收集了某城市居民年收入(所有居民在一年内收入的总和)与A商品销售额的10年数据,如表所示.画出散点图，判断成对样本数据是否线性相关，并通过样本相关系数推断居民年收入与A商品销售额的相关程度和变化趋势的异同.
人教版高中数学选择性必修二等比数列的概念 (2) 教学设计
二、典例解析例4. 用 10 000元购买某个理财产品一年.（1）若以月利率0.400%的复利计息，12个月能获得多少利息（精确到1元）？（2）若以季度复利计息，存4个季度，则当每季度利率为多少时，按季结算的利息不少于按月结算的利息（精确到10^(-5)）？分析：复利是指把前一期的利息与本金之和算作本金，再计算下一期的利息.所以若原始本金为a元，每期的利率为r ，则从第一期开始，各期的本利和a , a(1+r)，a(1+r)^2…构成等比数列.解：（1）设这笔钱存 n 个月以后的本利和组成一个数列{a_n }，则{a_n }是等比数列，首项a_1=10^4 (1+0.400%)，公比 q=1+0.400%，所以a_12=a_1 q^11 〖=10〗^4 (1+0.400%)^12≈10 490.7.所以，12个月后的利息为10 490.7-10^4≈491（元）.解：（2）设季度利率为 r ，这笔钱存 n 个季度以后的本利和组成一个数列{b_n }，则{b_n }也是一个等比数列，首项 b_1=10^4 (1+r)，公比为1+r，于是 b_4=10^4 (1+r)^4.
人教版高中数学选择性必修二等比数列的前n项和公式 (1) 教学设计
新知探究国际象棋起源于古代印度.相传国王要奖赏国际象棋的发明者，问他想要什么.发明者说：“请在棋盘的第1个格子里放上1颗麦粒，第2个格子里放上2颗麦粒，第3个格子里放上4颗麦粒，依次类推，每个格子里放的麦粒都是前一个格子里放的麦粒数的2倍，直到第64个格子.请给我足够的麦粒以实现上述要求.”国王觉得这个要求不高，就欣然同意了.假定千粒麦粒的质量为40克，据查，2016--2017年度世界年度小麦产量约为7.5亿吨，根据以上数据，判断国王是否能实现他的诺言.问题1：每个格子里放的麦粒数可以构成一个数列,请判断分析这个数列是否是等比数列?并写出这个等比数列的通项公式.是等比数列,首项是1，公比是2，共64项. 通项公式为〖a_n=2〗^(n-1)问题2：请将发明者的要求表述成数学问题.
人教版高中数学选择性必修二等差数列的概念（2）教学设计
二、典例解析例3.某公司购置了一台价值为220万元的设备，随着设备在使用过程中老化，其价值会逐年减少.经验表明，每经过一年其价值会减少d(d为正常数）万元.已知这台设备的使用年限为10年，超过10年 ，它的价值将低于购进价值的5%，设备将报废.请确定d的范围.分析：该设备使用n年后的价值构成数列{an}，由题意可知，an＝an－1－d (n≥2). 即：an－an－1＝－d.所以{an}为公差为－d的等差数列.10年之内（含10年），该设备的价值不小于（220×5%=）11万元；10年后，该设备的价值需小于11万元．利用{an}的通项公式列不等式求解．解：设使用n年后，这台设备的价值为an万元，则可得数列{an}．由已知条件，得an＝an－1－d（n≥2）．所以数列{an}是一个公差为－d的等差数列.因为a1＝220－d，所以an＝220－d＋(n－1)(－d)＝220－nd. 由题意，得a10≥11，a11＜11. 即：{█("220－10d≥11" @"220－11d＜11" )┤解得19<d≤20.9所以，d的求值范围为19<d≤20.9
人教版高中数学选择性必修二等比数列的前n项和公式 (2) 教学设计
二、典例解析例10. 如图，正方形ABCD 的边长为5cm ，取正方形ABCD 各边的中点E,F,G,H, 作第2个正方形 EFGH，然后再取正方形EFGH各边的中点I,J,K,L，作第3个正方形IJKL ，依此方法一直继续下去. (1) 求从正方形ABCD 开始，连续10个正方形的面积之和；(2) 如果这个作图过程可以一直继续下去，那么所有这些正方形的面积之和将趋近于多少？分析：可以利用数列表示各正方形的面积，根据条件可知，这是一个等比数列。解：设正方形的面积为a_1，后续各正方形的面积依次为a_2, a_(3, ) 〖…,a〗_n,…，则a_1=25,由于第k+1个正方形的顶点分别是第k个正方形各边的中点，所以a_(k+1)=〖1/2 a〗_k,因此{a_n}，是以25为首项，1/2为公比的等比数列.设{a_n}的前项和为S_n（1）S_10=(25×[1-(1/2)^10 ] )/("1 " -1/2)=50×[1-(1/2)^10 ]=25575/512所以，前10个正方形的面积之和为25575/512cm^2.(2)当无限增大时，无限趋近于所有正方形的面积和
人教版高中数学选择性必修二等差数列的前n项和公式（2）教学设计
课前小测1．思考辨析(1)若Sn为等差数列{an}的前n项和，则数列Snn也是等差数列．( )(2)若a1>0，d<0，则等差数列中所有正项之和最大．( )(3)在等差数列中，Sn是其前n项和，则有S2n－1＝(2n－1)an.( )[答案] (1)√ (2)√ (3)√2．在项数为2n＋1的等差数列中，所有奇数项的和为165，所有偶数项的和为150，则n等于( )A．9 B．10 C．11 D．12B [∵S奇S偶＝n＋1n，∴165150＝n＋1n.∴n＝10.故选B项．]3．等差数列{an}中，S2＝4，S4＝9，则S6＝________.15 [由S2，S4－S2，S6－S4成等差数列得2(S4－S2)＝S2＋(S6－S4)解得S6＝15.]4．已知数列{an}的通项公式是an＝2n－48，则Sn取得最小值时，n为________.23或24 [由an≤0即2n－48≤0得n≤24.∴所有负项的和最小，即n＝23或24.]二、典例解析例8.某校新建一个报告厅，要求容纳800个座位，报告厅共有20排座位，从第2排起后一排都比前一排多两个座位. 问第1排应安排多少个座位？分析：将第1排到第20排的座位数依次排成一列，构成数列{an} ，设数列{an} 的前n项和为S_n。