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新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计二
1. Ss look at the picture and scan the passage to understand the main idea while teacher is giving the following questions to inspire Ss to think.*Where are those people?*What are they doing?*Why are they so excited?2. Ss complete the passage with the appropriate -ing form. Then discuss and check the answers with class.Answers: boring, interesting, taking, exciting, amazing3. The teacher raises questions for the students to discuss and encourages them to express their opinions.*Do you like La Tomatina? Why or why not?4. Each group representative reports the discussion result, the teacher gives feedback and the evaluation.Step 6 PracticeActivity 41. Ss complete the Ex 2 in Using structures.2. Check the answers after finishing the exercises.①The dragon boat races are the most exciting part of the Dragon Boat Festival.② The children were excited to go Easter egg hunting.③What an amazing performance! This is the best music festival I have ever been to.④We were amazed by her funny-looking hat.⑤His inspiring speech at the conference won the admiration/ favour of the audience.⑥This is a challenging game to test your memory and observation capabilities. 3. T asks Ss to finish Ex 3 and 4 in Using structures by themselves, then check the answers with class.Step 6 Homework1. Understand and master the functions and usage of the -ing form;2. Finish the other exercises in Using structures.1、通过本节内容学习，学生是否理解和掌握动词-ing形式作定语和表语的功能和意义；2、通过本节内容学习，学生能否在理解文段内容的基础上，根据上下文语境和表达逻辑，能正确运用动词-ing形式描述节日庆典。3、通过本节内容学习，学生是否归纳和积累用于表达情绪的相关词汇。
新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计一
本板块的活动主题是“谈论节日活动”（Talk about festival activities），主要是从贴近学生日常生活的角度来切入“节日”主题。学生会听到发生在三个国家不同节日场景下的简短对话，对话中的人们正在参与或将要亲历不同的庆祝活动。随着全球化的进程加速，国际交流日益频繁，无论是国人走出国门还是外国友人访问中国，都已成为司空见惯的事情。因此，该板块所选取的三个典型节日场景都是属于跨文化交际语境，不仅每组对话中的人物来自不同的文化背景，对话者的身份和关系也不尽相同。1. Master the new words related to holiday: the lantern, Carnival, costume, dress(sb)up, march, congratulation, congratulate, riddle, ceremony, samba, make - up, after all. 2. To understand the origin of major world festivals and the activities held to celebrate them and the significance of these activities;3. Improve listening comprehension and oral expression of the topic by listening and talking about traditional festivals around the world;4. Improve my understanding of the topic by watching pictures and videos about different traditional festivals around the world;5. Review the common assimilation phenomenon in English phonetics, can distinguish the assimilated phonemes in the natural language flow, and consciously use the assimilation skill in oral expression. Importance:1. Guide students to pay attention to the attitude of the speaker in the process of listening, and identify the relationship between the characters;2. Inspire students to use topic words to describe the festival activities based on their background knowledge. Difficulties:In the process of listening to the correct understanding of the speaker's attitude, accurately identify the relationship between the characters.
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计二
Activity 41. Students complete the task of activity 4, then teachers and students check the answers. 2. The teacher organized the students to work together and asked them to use the tables and mind maps sorted out before to retold the important choices in Lin Qiaozhi's life and their resultsStep 5 Language points1. The teacher asks the students to read the text carefully, find out the core words and long and difficult sentences in the text and draw lines, understand the use of vocabulary, and analyze the structure of long and difficult sentences. 2. The teacher explains and summarizes the usage of core vocabulary and asks the students to take notes. 3. The teacher analyzes and explains the long and difficult sentences that the students don't understand, so that the students can understand them better. Step 6 Homework1. Read the text again, in-depth understanding of the text; 2. Master the use of core vocabulary and understand the long and difficult sentences. 3. Complete relevant exercises in the guide plan. 1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否结合文本特点总结林巧稚的人生原则和人格品质特征；3、通过本节内容学习，学生能否针对人生抉择发表自己的看法；能否全面地、客观地、理性地看待问题，进而对道德和人性有更加深入的思考和理解。
新人教版高中英语必修3Unit 1 Festivals and Celebrations教学设计三
*wide range of origins(= a great number of different origins, many kinds of origins)*It featured a parade and a great feast with music, dancing, and sports. (=A parade and a great feast with music, dancing, and sports were included as important parts of the Egyptian harvest festival.)*.. some traditions may fade away and others may be established.(= Some traditions may disappear gradually, while other new traditions may come into being.）Step 6 Practice(1) Listen and follow the tape.The teacher may remind the students to pay attention to the meaning and usage of the black words in the context, so as to prepare for the completion of the blanks in activity 5 and vocabulary exercises in the exercise book.(2) Students complete the text of activity 5 by themselves.The teacher needs to remind the students to fill in the blanks with the correct form of the vocabulary they have learned in the text.Students exchange their answers with their partners, and then teachers and students check their answers.(3)Finish the Ex in Activity 5 of students’ book.Step 7 Homework1. Read the text again, in-depth understanding of the text;2. Discuss the origin of festivals, the historical changes of related customs, the influence of commercial society on festivals and the connotation and essential meaning of festivals.3. Complete relevant exercises in the guide plan.1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否结合文本特点快速而准确地找到主题句；3、通过本节内容学习，学生能否理清论说文的语篇结构和文本逻辑，了解节日风俗发展与变迁，感悟节日的内涵与意义。
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计四
3.Teachers ask different groups to report the answers to the questions and ask them to try different sentence patterns.The teacher added some sentence patterns for students to refer to when writing.Step 4 Writing taskActivity 51.Write the first draft.Students first review the evaluation criteria in activity 5, and then independently complete the draft according to the outline of activity 4, the answers to the questions listed in the group discussion and report, and the reference sentence pattern.2.Change partners.The teacher guides the students to evaluate their partner's composition according to the checklist of activity 5 and proposes Suggestions for modification.3.Finalize the draft.Based on the peer evaluation, students revise their own compositions and determine the final draft.Finally, through group recommendation, the teacher selects excellent compositions for projection display or reading aloud in class, and gives comments and Suggestions.Step 5 Showing writingActivity 5T call some Ss to share their writing.Step 6 Homework1. Read the passage in this section to better understand the passage.2. Carefully understand the hierarchical structure of the article, and deeply understand the plot of the story according to the causes, process and results;3. Independently complete the relevant exercises in the guide plan.1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否通过人物言行的对比分析道德故事的深层内涵；3、通过本节内容学习，学生能否根据故事的起因、经过和结果来深入理解故事的情节，从而了解文章的层次结构；4、结合现实生活案例发表自己的见解和看法,写一篇观点明确、层次分明的故事评论。
新人教版高中英语必修3Unit 3 Diverse Cultures教学设计三
The price is the same as(the price was)before the war.价格与战前相同。(4)定语从句中的“关系代词＋助动词be”可以省略。The ticket(that/which was)booked by his sister has been sent to him.他妹妹订的那张票已送到了他那里。Step 5 PracticeActivity 3(1) Guide students to complete the four activities in the Using Structures part of exercise book, in which activities 1 and 2 focus on ellipsis in dialogue answers, activity 3 focus on signs and headlines, two typical situations where ellipsis is used, and activity 4 focus on ellipsis in diary, an informal style.(2) Combine the examples in the above activities, ask students to summarize the omitted situations in groups, and make their own summary into a poster, and post it on the class wall after class to share with the class.(This step should give full play to the subjectivity of students, and teachers should encourage students to conclude different ellipsis phenomena according to their own understanding, they can conclude according to the different parts omitted in the sentence.)Step 6 Homework1. Understand and master the usages of ellipsis;2. Finish the other exercises in Using structures of Workbook.1、通过本节内容学习，学生是否理解和掌握省略的用法；2、通过本节内容学习，学生能否根据上下文语境或情景恢复句子中省略的成分，体会使用省略的效果；3、通过本节内容学习，学生能否独立完成练习册和导学案中的相关练习。
新人教版高中英语必修3Unit 3 Diverse Cultures教学设计二
(2)Consolidate key vocabulary.Ask the students to complete the exercises of activity 6 by themselves. Then ask them to check the answers with their partners.(The first language:Damage of the 1906 San Francisco earthquake and fire.A second language: Yunnan - one of the most diverse provinces in China).Step 5 Language points1. The teacher asks the students to read the text carefully, find out the more words and long and difficult sentences in the text and draw lines, understand the use of vocabulary, and analyze the structure of long and difficult sentences.2. The teacher explains and summarizes the usage of core vocabulary and asks the students to take notes.3. The teacher analyzes and explains the long and difficult sentences that the students don't understand, so that the students can understand them better.Step 6 Homework1. Read the text again, in-depth understanding of the text;2. Master the use of core vocabulary and understand the long and difficult sentences.3. Complete relevant exercises in the guide plan.1、通过本节内容学习，学生是否理解和掌握阅读文本中的新词汇的意义与用法；2、通过本节内容学习，学生能否结合文本特点了解文章的结构和作者的写作逻辑；3、通过本节内容学习，学生能否了解旧金山的城市风貌、文化特色，以及加利福尼亚州的历史，体会多元文化对美国的影响。
新人教版高中英语必修3Unit 3 Diverse Cultures教学设计四
该板块的活动主题是“介绍一个有显著文化特征的地方”( Describe a place with distinctive cultural identity)。该板块通过介绍中国城继续聚焦中国文化。本单元主题图呈现的是旧金山中国城的典型景象, Reading and Thinking部分也提到中国城,为该板块作铺垫。介绍中国城的目的主要是体现中国文化与美国多元文化的关系,它是美国多元文化的重要组成部分。中国城也是海外华人的精神家园和传播中国文化的重要窗口,外国人在中国城能近距离体验中国文化。1. Read the text to understand the cultural characteristics of Chinatown in San Francisco and the relationship between Chinese culture and American multiculturalism;2. Through reading, learn to comb the main information of the article, understand the author's writing purpose and writing characteristics;3. Learn to give a comprehensive, accurate, and organized description of the city or town you live in;Learn to revise and evaluate your writing.Importance:1. Guide the students to read the introduction of Chinatown in San Francisco and grasp its writing characteristics;2. Guide students to introduce their city or town in a comprehensive, accurate and organized way;3. Learn to comb the main information of the article, understand the author's writing purpose, and master the core vocabulary.
新人教版高中英语必修3Unit 2 Morals and Virtues教学设计三
The joke set her crying.这个玩笑使她哭起来。Step 5 ReadingActivity 31. Students read the small text in activity 3. The teacher provides several small questions to check whether students understand the content of the text and the ideographic function of the -ing form in the text.*Where are those people?*Why did Dr Bethune come to China?*How did he help the Chinese people during the war?*What did Chairman Mao Zedong say about him?2. Ss try to rewrite some sentences using the -ing form. Then check the answers. When checking the answers, the teacher can ask different students to read the rewritten sentences and give comments.Answers:1. he became very interested in medicine, deciding to become a doctor.2. …after hearing that many people were dying in the war.3. Helping to organise hospitals, he taught doctors and nurses, and showed people how to give first aid./ He helped to organise hospitals, teaching doctors and nurses, and showing people how to give first aid.4. …praising Dr Bethune as a hero to be remembered in China.Step 6 PracticeActivity 4Students complete grammar activities 2 and 3 on page 69 of the workbook.Step 6 Homework1. Understand and master the functions and usage of the -ing form;2. Finish the other exercises in Using structures.1、通过本节内容学习，学生是否理解和掌握动词-ing形式作宾语补足语语和状语语的功能和意义；2、通过本节内容学习，学生能否正确使用动词-ing形式描述人物的行为、动作及其经历；3、通过本节内容学习，学生能否独立完成练习册和导学案中的相关练习。
新人教版高中英语必修3Unit 2 Morals and virtues教学设计一
(2) students are divided into groups according to the requirements of activity 3. Each student shares a story of personal experience or hearing-witnessing kindness, and then selects the most touching story in the group and shares it with the whole class. Before the students share the story, the teacher can instruct them to use the words and sentence patterns in the box to express. For example, the words in the box can be classified:Time order: first of all, then, after that, later, finally logical relationship :so, however, although, butTeachers can also appropriately add some transitional language to enrich students' expression:Afterwards, afterwards, at last, in the end, eventuallySpatial order: next to, far from, on the left, in front ofOtherwise, nevertheless, as a result, therefore, furthermore, in addition, as well asSummary: in a word, in short, on the whole, to sum up, in briefStep 8 Homework1. Understand the definition of "moral dilemma" and establish a correct moral view;2. Accumulate vocabulary about attitudes and emotions in listening texts and use them to express your own views;3. Complete relevant exercises in the guide plan.1、通过本节内容学习，学生能否理解理解“道德困境”的定义；2、通过本节内容学习，学生能否通过说话人所表达的内容、说话的语气、语调等来判断其态度和情绪；3、通过本节内容学习，学生能否针对具体的道德困境发表自己的看法和见解，能否掌握听力理训练中的听力策略。
新人教版高中英语必修3Unit 3 Diverse Cultures教学设计一
Activity 81.Grasp the main idea of the listening.Listen to the tape and answer the following questions:Who are the two speakers in the listening? What is their relationship?What is the main idea of the first part of the listening? How about the second part?2.Complete the passage.Ask the students to quickly review the summaries of the two listening materials in activity 2. Then play the recording for the second time.Ask them to complete the passage and fill in the blanks.3.Play the recording again and ask the students to use the structure diagram to comb the information structure in the listening.(While listening, take notes. Capture key information quickly and accurately.)Step 8 Talking Activity 91.Focus on the listening text.Listen to the students and listen to the tape. Let them understand the attitudes of Wu Yue and Justin in the conversation.How does Wu Yue feel about Chinese minority cultures?What does Justin think of the Miao and Dong cultures?How do you know that?2.learn functional items that express concerns.Ask students to focus on the expressions listed in activity. 3.And try to analyze the meaning they convey, including praise (Super!).Agree (Exactly!)"(You're kidding.!)Tell me more about it. Tell me more about it.For example, "Yeah Sure." "Definitely!" "Certainly!" "No kidding!" "No wonder!" and so on.4.Ask the students to have conversations in small groups, acting as Jsim and his friends.Justin shares his travels in Guizhou with friends and his thoughts;Justin's friends should give appropriate feedback, express their interest in relevant information, and ask for information when necessary.In order to enrich the dialogue, teachers can expand and supplement the introduction of Miao, dong, Lusheng and Dong Dage.After the group practice, the teacher can choose several groups of students to show, and let the rest of the students listen carefully, after listening to the best performance of the group, and give at least two reasons.
高中语文人教版必修二《归园田居》说课稿
一、说教材本节课选自于人教版语文必修二第二单元诗三首中的一首诗歌，它是陶渊明归隐后的作品。写的是田园之乐，实际表明的是作者不愿与世俗同流合污的心声，甘愿守着自己的拙志回归田园。学习该诗，有助于学生了解山水田园诗的特点，感受者作者不同流俗的高尚情操，同时可以培养学生初步的鉴赏古典诗歌的能力。
人教版高中生物必修3第六章第一节《人口增长对生态环境的影响》说课稿
3、讨论问题二：我国、我市人口增长对环境有那些影响？教师：让第三、第四组学生分别介绍、展示课前调查到的资料，说明人口增长对我国环境的影响、对三亚市环境的影响。学生：第三组学生派代表介绍人口增长过快对我国生态环境的影响。第四小组由学生自己主持“我市人口增长过快对三亚市生态环境的影响”讨论会，汇报课前调查到的资料和讨论，其它小组参与发言。教师：投影：课本图6－2组织学生讨论、补充和完善。学生：观察老师投影图片并进行讨论，对图片问题进行补充和完善。教学意图：通过让学生汇报、观察、主持，能让学生亲身体验，更深刻地理解人口增长对生态环境的影响，培养和提高学生的表达能力、观察能力、主持会议的能力。4、讨论问题三：怎样协调人与环境的关系?教师：组织第五组学生进行汇报课前调查到的资料，交流、讨论、发表意见和见解。学生：展示课件、图片，汇报调查到的情况，提出合理建议。
第八周国旗下讲话稿：高度的自制力是成功的基本要素
春天悄然而知，春风轻轻地吹红了鲜花，春雨也静静地润绿了大地，蓬勃的你们正像那红花绿叶一样鲜活，一样有生命力。而在这样一个美丽的季节里，我带给大家的是一句忠告：那就是高度的自制力是成功的基本要素。说热忱是促使你采取行动的重要动力，而自治则是指引你行动方向的平衡轮。有一个故事是这样的：一个商人需要一个伙计，他便在窗户上贴上了一张独特的广告：招聘一个能自我克制的男士，每星期4美元，合适者可以拿6美元。“自我克制”这个术语在村子里引起了议论，自然引起了小伙子们、家长们的思考，同样也引来了众多的求职者。而每个求职者都要经过一个测试。“能阅读吗？”“能，先生”“你能读一读这一段吗？”他把一张报纸放到小伙子的面前“可以，先生”“你能一刻不停的朗读吗？”“可以，先生”“很好，请跟我来”商人把他带到他的私人办公室，然后关上门，他把报纸送到小伙子手中，上面写着他答应一刻不停地读完的那段话，阅读刚开始，商人就放出六只可爱的小狗，小狗跑到男孩的脚边，“这太过分了”男孩经受不住诱惑，要看看美丽的小狗，由于视线离开了阅读的材料，男孩忘记了自己的角色，读错了，当然他也就失去了这个机会。
点到直线的距离公式教学设计人教A版高中数学选择性必修第一册
4.已知△ABC三个顶点坐标A(－1,3)，B(－3,0)，C(1,2)，求△ABC的面积S.【解析】由直线方程的两点式得直线BC的方程为 ＝ ，即x－2y＋3＝0，由两点间距离公式得|BC|＝ ，点A到BC的距离为d，即为BC边上的高，d＝ ，所以S＝ |BC|·d＝ ×2 × ＝4，即△ABC的面积为4.5.已知直线l经过点P(0,2),且A(1,1),B(-3,1)两点到直线l的距离相等,求直线l的方程.解:(方法一)∵点A(1,1)与B(-3,1)到y轴的距离不相等,∴直线l的斜率存在,设为k.又直线l在y轴上的截距为2,则直线l的方程为y=kx+2,即kx-y+2=0.由点A(1,1)与B(-3,1)到直线l的距离相等,∴直线l的方程是y=2或x-y+2=0.得("|" k"-" 1+2"|" )/√(k^2+1)=("|-" 3k"-" 1+2"|" )/√(k^2+1),解得k=0或k=1.(方法二)当直线l过线段AB的中点时,A,B两点到直线l的距离相等.∵AB的中点是(-1,1),又直线l过点P(0,2),∴直线l的方程是x-y+2=0.当直线l∥AB时,A,B两点到直线l的距离相等.∵直线AB的斜率为0,∴直线l的斜率为0,∴直线l的方程为y=2.综上所述,满足条件的直线l的方程是x-y+2=0或y=2.
两点间的距离公式教学设计人教A版高中数学选择性必修第一册
一、情境导学在一条笔直的公路同侧有两个大型小区,现在计划在公路上某处建一个公交站点C,以方便居住在两个小区住户的出行.如何选址能使站点到两个小区的距离之和最小?二、探究新知问题1.在数轴上已知两点A、B，如何求A、B两点间的距离？提示：|AB|＝|xA－xB|.问题2：在平面直角坐标系中能否利用数轴上两点间的距离求出任意两点间距离？探究.当x1≠x2，y1≠y2时，|P1P2|＝？请简单说明理由．提示：可以，构造直角三角形利用勾股定理求解．答案：如图，在Rt △P1QP2中，|P1P2|2＝|P1Q|2＋|QP2|2，所以|P1P2|＝?x2－x1?2＋?y2－y1?2.即两点P1(x1，y1)，P2(x2，y2)间的距离|P1P2|＝?x2－x1?2＋?y2－y1?2.你还能用其它方法证明这个公式吗？2．两点间距离公式的理解(1)此公式与两点的先后顺序无关，也就是说公式也可写成|P1P2|＝?x2－x1?2＋?y2－y1?2.(2)当直线P1P2平行于x轴时，|P1P2|＝|x2－x1|.当直线P1P2平行于y轴时，|P1P2|＝|y2－y1|.
两条平行线间的距离教学设计人教A版高中数学选择性必修第一册
一、情境导学前面我们已经得到了两点间的距离公式，点到直线的距离公式，关于平面上的距离问题，两条直线间的距离也是值得研究的。思考1：立定跳远测量的什么距离？A.两平行线的距离 B.点到直线的距离 C. 点到点的距离二、探究新知思考2：已知两条平行直线l_1,l_2的方程，如何求l_1 〖与l〗_2间的距离？根据两条平行直线间距离的含义，在直线l_1上取任一点P（x_0,y_0 ），,点P（x_0,y_0 ）到直线l_2的距离就是直线l_1与直线l_2间的距离，这样求两条平行线间的距离就转化为求点到直线的距离。两条平行直线间的距离1. 定义：夹在两平行线间的__________的长.公垂线段2. 图示： 3. 求法：转化为点到直线的距离.1．原点到直线x＋2y－5＝0的距离是( )A．2 B．3 C．2 D．5D [d＝|－5|12＋22＝5.选D.]
两直线的交点坐标教学设计人教A版高中数学选择性必修第一册
1.直线2x+y+8=0和直线x+y-1=0的交点坐标是( )A.(-9,-10) B.(-9,10) C.(9,10) D.(9,-10)解析:解方程组{■(2x+y+8=0"," @x+y"-" 1=0"," )┤得{■(x="-" 9"," @y=10"," )┤即交点坐标是(-9,10).答案:B 2.直线2x+3y-k=0和直线x-ky+12=0的交点在x轴上,则k的值为( )A.-24 B.24 C.6 D.± 6解析:∵直线2x+3y-k=0和直线x-ky+12=0的交点在x轴上,可设交点坐标为(a,0),∴{■(2a"-" k=0"," @a+12=0"," )┤解得{■(a="-" 12"," @k="-" 24"," )┤故选A.答案:A 3.已知直线l1:ax+y-6=0与l2:x+(a-2)y+a-1=0相交于点P,若l1⊥l2,则点P的坐标为 . 解析:∵直线l1:ax+y-6=0与l2:x+(a-2)y+a-1=0相交于点P,且l1⊥l2,∴a×1+1×(a-2)=0,解得a=1,联立方程{■(x+y"-" 6=0"," @x"-" y=0"," )┤易得x=3,y=3,∴点P的坐标为(3,3).答案:(3,3) 4.求证:不论m为何值,直线(m-1)x+(2m-1)y=m-5都通过一定点. 证明:将原方程按m的降幂排列,整理得(x+2y-1)m-(x+y-5)=0,此式对于m的任意实数值都成立,根据恒等式的要求,m的一次项系数与常数项均等于零,故有{■(x+2y"-" 1=0"," @x+y"-" 5=0"," )┤解得{■(x=9"," @y="-" 4"." )┤
圆的标准方程教学设计人教A版高中数学选择性必修第一册
(1)几何法它是利用图形的几何性质,如圆的性质等,直接求出圆的圆心和半径,代入圆的标准方程,从而得到圆的标准方程.(2)待定系数法由三个独立条件得到三个方程,解方程组以得到圆的标准方程中三个参数,从而确定圆的标准方程.它是求圆的方程最常用的方法,一般步骤是:①设——设所求圆的方程为(x-a)2+(y-b)2=r2;②列——由已知条件,建立关于a,b,r的方程组;③解——解方程组,求出a,b,r;④代——将a,b,r代入所设方程,得所求圆的方程.跟踪训练1．已知△ABC的三个顶点坐标分别为A(0,5)，B(1，－2)，C(－3，－4)，求该三角形的外接圆的方程．[解] 法一：设所求圆的标准方程为(x－a)2＋(y－b)2＝r2.因为A(0,5)，B(1,－2)，C(－3,－4)都在圆上，所以它们的坐标都满足圆的标准方程，于是有?0－a?2＋?5－b?2＝r2，?1－a?2＋?－2－b?2＝r2，?－3－a?2＋?－4－b?2＝r2.解得a＝－3，b＝1，r＝5.故所求圆的标准方程是(x＋3)2＋(y－1)2＝25.
圆的一般方程教学设计人教A版高中数学选择性必修第一册
情境导学前面我们已讨论了圆的标准方程为(x-a)2+(y-b)2=r2,现将其展开可得：x2+y2-2ax-2bx+a2+b2-r2=0.可见,任何一个圆的方程都可以变形x2+y2+Dx+Ey+F=0的形式.请大家思考一下,形如x2+y2+Dx+Ey+F=0的方程表示的曲线是不是圆?下面我们来探讨这一方面的问题.探究新知例如,对于方程x^2+y^2-2x-4y+6=0,对其进行配方，得〖(x-1)〗^2+(〖y-2)〗^2=-1,因为任意一点的坐标 (x,y) 都不满足这个方程，所以这个方程不表示任何图形，所以形如x2+y2+Dx+Ey+F=0的方程不一定能通过恒等变换为圆的标准方程，这表明形如x2+y2+Dx+Ey+F=0的方程不一定是圆的方程.一、圆的一般方程（1）当D2+E2-4F>0时,方程x2+y2+Dx+Ey+F=0表示以(-D/2,-E/2)为圆心,1/2 √(D^2+E^2 "-" 4F)为半径的圆,将方程x2+y2+Dx+Ey+F=0，配方可得〖(x+D/2)〗^2+(〖y+E/2)〗^2=(D^2+E^2-4F)/4（2）当D2+E2-4F=0时,方程x2+y2+Dx+Ey+F=0，表示一个点(-D/2,-E/2)（3）当D2+E2-4F0);