若a,b属于R，a^2+b^2-ab=2，求ab最小值？_百度知道
若a,b属于R，a^2+b^2-ab=2，求ab最小值？
我有更好的答案
3;3且a²=2/3)=-2/=4(2-x²3得ab≥2-(8/=8y²=8-3x²,且0≤x²≤8&#47,y=a+b4(a²)即ab=2-x²≤8/34ab=(a+b)²-(a-b)²=y²-x²=(8-3x²)-x²,其中0≤x²+y²-ab)=3(a-b)²+(a+b)²得3x²+b&#178设x=a-b,且b=-a时取“=”所以ab的最小值是-2&#47
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ab的最小值是-2&#47已知a，b∈R，则：(a+b)²3所以;=ab+2代入①得到：(ab+2)+2ab≥0==& 3ab+2≥0==& ab≥-2/+b²+b&#178，所以：a²-ab=2;+2ab≥0……………………………………①已知a²+b² a²≥0==&gt
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3所以;+b&#178解：已知a，b∈R，则：(a+b)&#178，ab的最小值是-2/=ab+2代入①得到：(ab+2)+2ab≥0==& 3ab+2≥0==& ab≥-2/+b&#178，所以：a²-ab=2;+2ab≥0……………………………………①已知a²+b² a²≥0==&gt
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＞＞＞Everyone knows it except .[ ]A. you and I B. I and you C...
Everyone knows it except&&&&&&&&&&&&& .
A. you and I B. I and you C. you and me D. me and you
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据魔方格专家权威分析，试题“Everyone knows it except .[ ]A. you and I B. I and you C...”主要考查你对&&人称代词&&等考点的理解。关于这些考点的“档案”如下：
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因为篇幅有限，只列出部分考点，详细请访问。
人称代词：人称代词是用来表示人的代词，有单数和复数之分，有主格和宾格之分。人称代词的主格在句中作主语;人称代词的宾格在句中作宾语，也可作动词或介词的宾语。　　主格：I, we, you, he, she, it, they在句子中作主语宾格：me, us, you, him, her, it, them在句子中作宾语He and I are in the same class. 我和他在同一个班级。Can you see them in the street? 你能看见他们在街上吗?人称代词在句中的作用：1）主格作主语。如：I am Chinese.我是中国人。2）宾格作宾语，放在及物动词或介词之后，有时还可以在口语中用作表语。如：①I don't know her.我不认识她。（动词宾语）②What's wrong with it?它怎么了？（介词宾语）③-Open the door,please.3）作表语作表语一般用主格， 但在口语中也常用宾格I saw at once it was her.我一下子看到了她。It's me.请开门，是我。（表语）4）作同位语作同位语是用宾格We ,us ,there,will be able to fulfill the task.我们三人就能完成这项任务。主宾格的替换:一、宾格代替主格a.在简短对话中，当人称代词单独使用或在not后，多用宾语。　　---- I like English.　--我喜欢英语。　　---- Me too.　--我也喜欢。　　---- Have more wine?　--再来点酒喝吗?　　---- Not me.　--我可不要了。b.在表示比较的非正式的文体中，常用宾格代替主格。但如果比较状语的谓语保留，则主语只能用主格。　　He is taller than I/me.　　He is taller than I am.二、主格代替宾格a.在介词but，except后，有时可用主格代替宾格。b.在电话用语中常用主格。　　---- I wish to speak to Mary. --我想和玛丽通话。　　---- This is she.　--我就是玛丽。注意：在动词be或to be后的人称代词视其前面的名词或代词而定。　　I thought it was she.　我以为是她。　（主格----主格）　　I thought it to be her.　（宾格----宾格）　　I was taken to be she.　我被当成了她。　（主格----主格）They took me to be her.他们把我当成了她。　（宾格----宾格）人称代词用法：一、人称代词的宾格在句中作宾语，往往用在动词或介词后面。例:1.Listen to me,Dad.2.Peter is sitting behind me.3.Let me got here now.4.Give me an orange,please.二、you既是"你"或"你们"的主格，又是它们的宾格；her既是"她"的所有格，又是它的宾格。我们可以根据它们在句子中的位置来判断它们属于主格、所有格还是宾格。三、and是一个我们常用来连接两个词的连接词。它虽然与介词with有同样的意思，但它的前后可以是人称代词的主语，也可以是人称代词的宾格，而with只能跟人称代词的宾格。如：You and I are going to school.　　You are going to school with me.四、第三人称代词单数：er,sie,es 及 复数 sie 可指代人或物以及其它抽象概念等。此时，它们的性，数，格要与被指代的名词一致。人称代词用法口诀：人称代词分主/宾，只有八对要区分。你（们）、它主/宾同一形，其余主/宾须分清。谓语之前主格填，动/介之后宾格跟，口语运用最灵活，表语也可用宾格。人称代词并列现，注意顺序礼貌见，二一、三一、二三一，第一人称最谦虚，若把错误责任担，第一人称须当先。动前主格动后宾，名前形容介后宾；如果名词含在内，选用名物代就行。
人称代词并列用法的排列顺序：1）单数人称代词并列作主语时，其顺序为：第二人称→第三人称→第一人称即：you and I;he/she/itandI;you,he/she/it and I2）复数人称代词作主语时，其顺序为：第一人称→第二人称→第三人称即：we，you and they人称代词的变格形式：
them人称代词的形式：在一般现在时中，当主语是第三人称单数时，谓语动词要用第三人称单数形式，即常在动词原形后加-s或-es 　一、人称代词he,she,it是第三人称单数。如：　He likes watching TV. 他喜欢看电视。　She has lunch at twelve. 她十二点吃午餐。　It looks like a cat. 它看起来像只猫。　二、单个人名、地名或称呼作主语；是第三人称单数。如：　①Han Mei looks like her mother. 韩梅看起来像她的母亲。　②Beijing is in China. 北京在中国。　③Uncle Wang often makes cakes. 王叔叔经常做蛋糕。　三、单数可数名词或"this / that / the+单数可数名词"作主语时，是第三人称单数。如：　①A horse is a useful animal. 马是有用的动物。　②This book is yours. 这本书是你的。　③That car is red. 那辆小汽车是红色的。　④The cat is Lucy's. 这只猫是露茜的。　四、不定代词someone,somebody,nobody,everything,something等及指示代词this,that作主语时，是第三人称单数。如：　①Everyone is here. 大家到齐了。　②There is something wrong with the watch. 这块手表有毛病。　③This is a pen. 这是一支钢笔。　④That is an eraser. 那是一块橡皮擦。　五、不可数名词作主语时为第三人称单数。如：　①The milk is in the glass. 牛奶在玻璃杯里。　②The bread is very small. 那面包很小。　六、当数字或字母作主语时，看作第三人称单数。如：　①"6" is a lucky number. "6"是个吉利数字。　②"I" is a letter. "I"是个字母。
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新概念英语第二册lesson 48 Did you want to tell me som
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(单词翻译:双击或拖选)
&&& Lesson 48:Did you want to tell me something?
&&&&&&&&&& 你想对我说什么吗？
&&& First listen and then answer the question.
&&& 听录音，然后回答以下问题。
&&& Why did the writer become very worried?
&&& Dentists always ask questions when it is impossible for you to answer. My dentist had just pulled out one of my teeth and had told me to rest for a while. I tried to say something, but my mouth was full of cotton wool. He knew I collected match boxes and asked me whether my collection was growing. He then asked me how my brother was and whether I liked my new job in London. In answer to these questions I either nodded or made strange noises. Meanwhile, my tongue was busy searching out the hole where the tooth had been. I suddenly felt very worried, but could not say anything. When the dentist at last removed the cotton wool from my mouth, I was able to tell him that he had pulled out the wrong tooth.
New words and expressions 生词和短语
pull& v. 拔
cotton wool 药棉
collect& v. 搜集
collection& n. 收藏品，收集品
nod& v. 点头
meanwhile& adv. 同时
&&& 牙科医生们总是在你无法作出回答的时候向你提出问题。我的牙科医生刚刚给我拔掉了一颗牙，叫我休息一会儿。我想说点什么，但我嘴里塞满了药棉。他知道我收集火柴盒，于是问我收藏的火柴盒是否在增加。接着他又问我的兄弟近来如何，问我是否喜欢伦敦的新工作。作为对这些问题的回答，我不是点头，就是发出奇怪的声音。与此同时，我的舌头正在忙着寻找刚拔掉的那颗牙的伤口。我突然非常着急起来，但却什么也说不出来。当那位牙医最后将药棉从我嘴中取出时，我总算有可能告诉他，他拔错了牙。
　　自学导读
1．Dentists always ask questions when it is impossible for you to answer. 牙科医生们总是在你无法作出回答的时候向你提出问题。
在when引导的时间状语从句中，it为先行主语，代指后面的不定式，for+人称代词／名词说明不定式表示的动作是谁做的：
It is not hard for you to help them.
你帮助他们并不难。
It was a mistake for me to come to the party.
我来参加晚会是错误的。
impossible通常不以人作主语，而以不定式或从句作主语：
It is impossible for him to help you.
他不可能帮你。
It is impossible that he will help you.
（译文同上）
2．In answer to these questions I either nodded or made strange noises. 作为对这些问题的回答，我不是点头，就是发出奇怪的声音。
（1）in answer to为固定短语，在这里表示&作为对&&的回答&：
In answer to my question, Dan shook his head.
作为对我的问题的回答，丹摇了摇头。
这个短语的另一个含义是&响应&&的请求&：
In answer to my request, he wrote a letter to George.
应我的请求，他给乔治写了封信。
（2）made strange noises, 发出奇怪的声音。&我&并不是有意发出这些声音，而是因为嘴里有药棉，又想回答医生的话造成的。
3．Meanwhile, my tongue was busy searching out the hole where the tooth had been. 与此同时，我的舌头正在忙着寻找刚拔掉的那颗牙的伤口。
（1）副词meanwhile表示&在此期间&、&与此同时&：
He won't come until ten o'clock. Meanwhile you can have a rest.
他10点以前不会来。在此期间你可以休息一下。
Mary was talking to me about her new dress. Meanwhile I was thinking about something else.
玛丽在和我讲她的新衣服。与此同时我却在想着其他事情。
（2）search out表示&找出&、&查出&、&搜出&等：
Have you searched out the books I needed?
你找出我需要的书了吗？
（3）where the tooth had been用的是过去完成时，因为在描述这件事的时候那颗牙已经不在了。牙齿尚在的时间是&过去的过去&。
4．When the dentist at last removed the cotton wool from my mouth&
当那位牙医最后将药棉从我嘴中取出时&&
remove可以表示&拿去&、&除去&、&去掉&，通常结构为&remove +名词+from&；它也可以单独使用：
I've removed that picture from the wall.
我已经把那幅画从墙上拿走了。
Please remove your hat.
请摘下你的帽子。
　　语法 Grammar in use
复习第26～45课的部分语法
It is one of the ugliest faces(that) I have ever seen.
这是我见过的最丑陋的头像之一。（that在关系从句中作宾语，可省略）
There aren't many students who sing as well as she does.
在学生当中没几个人唱歌像她那么好。（who在关系从句中作主语，不可省略）
People are not so honest as they once were.
人们不再像以前那样诚实了。（not so/ as&as用于比较状语从句）
He had hardly had time to
down when he sold the house.
他还没等安顿下来就卖掉了房子。（hardly&when用于过去完成时）
No sooner had I sat down than he came in.
我刚坐下他就进来了。（no sooner&than用于过去完成时；否定词位于句首时句子要倒装）
The box was so heavy that she couldn't lift it.
箱子太重了，她搬不起来。（so+形容词+that表示&如此&&以至于&）
The thief got such a
that he dropped the bag.
那个小偷吓得把提包都扔了。（such〈a〉+名词+that表示&如此&&以至于&）
Billy is not at home at present. He's at school.
比利现在不在家，他在学校。（at+名词的用法）
　　词汇学习 Word study
1．pull vt.,vi.
（1）拉，拖，牵，扯：
I felt someone pulling my arm.
我觉得有人在拉我的胳膊。
They pulled the heavy bag into a room.
他们把那个重袋子拖到一个房间里。
You have to pull hard.
你得用力拉。
（2）拔，抽：
You've pulled out the wrong teeth!
你拔错了牙！
He pulled an address book from his pocket.
他从口袋里抽出一本通讯录。
（1）vt.,vi. 点头，点头示意／招呼：
I asked him if he wanted to come and he nodded his head.
我问他是否想来，他点了点头。
When we meet each other in the office, he always nods at me.
我们在办公室见面时，他总是向我点头打招呼。
（2）vi. 打盹，打瞌睡（常与off连用）：
He used to nod off during the French class.
他过去常在上法语课时打瞌睡。
As he was very tired, he nodded over his reading.
因为他很累，所以他一边看书一边打盹。
　　练习答案 Key to written exercises
1．难点练习答案
A 1 which&&&&&&&&&&&&& 2 denied&&&&&&&&&&&&&&& 3 fetched
4 too&&&&&&&&&&&&&&&& 5 jobs&&&&&&&&&&&&&&&&&& 6 One&a&who
7 past&&&&&&&&&&&&&&& 8 next&&&&&&&&&&&&&&&& 9 watching
10 continually&&&& 11 remarked&&&&&&&&& 12
B (sample sentences)
I'm sorry to cause you such trouble.
Have you ever seen such beautiful pictures before? It's such a nice day that we can't stay !
I'm feeling so tired that I shall have to stop work.
C 1 He had no sooner come home than they rang him up from the office.
2 The plane had no sooner taken off than it returned to the airport.
D 1 made& 2 do& 3 make& 4 do& 5 Do& 6 make 7 made8 does
E 1 out& 2 up& 3 up& 4 up&away& 5 up& 6 out 7 back& 8 up with& 9 up with
F (sample sentences)
If you don't stop that noise at once, you'll have to go to bed. I'm at a
to know what to do.
It's stopped raining at last!
He's very busy and can't accept any more work at present. I'll be at home tonight.
2．多项选择题答案
1c& 2b& 3c& 4b& 5a& 6c
7b& 8 b& 9 d& 10 a& 11b& 12 c
　　课堂笔记
be busy doing 忙于做某事
search out找出
判断是否是定语从句就看是否和前面的名词有关系
where＝介词＋which
that is the house which i lived in
that is the house where i lived
this is the river where i swim
where作定语从句的标志，修饰前面的hole
in answer to作为对...的回答
in return for作为对...的报答
点击收听单词发音&&
vi.安家；定居；停留；vt.使定居；安排；解决
参考例句：
I have to settle my affairs before leaving here.离开这儿以前，我得把一些私人的事情安排妥当。
She has decided how she should settle the matter.她已做出决定如何来了解这件事。
n.惊骇；吃惊
参考例句：
A tree fell on the house and gave him a fright.一棵树倒在房子上，吓了他一大跳。
She turned pale with fright.她吓得面色刷白。
v.抢夺( rob的过去式和过去分词 )；抢劫；掠夺；使丧失
参考例句：
Would you be able to identify the man who robbed you? 你能够认出那个抢你东西的人吗？ 来自《简明英汉词典》
They stood looking on while the man was robbed. 正当那个人被抢劫时，他们却站在那儿袖手旁观。 来自《简明英汉词典》
adv.(在)室内，(在)户内
参考例句：
Because of the coldness of the weather we stayed indoors.我们因天气寒冷呆在家里。
It is very cold outside,you'd better come indoors across the board.外面很冷，你们所有人最好都进屋。
n.损失，遗失，失败，输，浪费，错过，[军]伤亡，降低
参考例句：
His death was a great loss to the country.他的逝世对这个国家是一大损失。
Because of the continued loss,the factory closed down.由于连续亏损，工厂关闭了。
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