比较大小PPT教学课件

Look at the photo and skim the story to find out: 1. What is the main topic of the story?
2.BWohdeyrleaanrgeuaDgeeb.bie and Simon?
They are at work, in the office of a travel agency.
实际生活中的问题。
作业布置
1、已知 x , y R, P 2x2 y 3,Q 2x y2 4
试比较P，Q的大小.
2、已知 a b c ，试比较 a2b b2c c2a 与 ab2 bc2 ca2 的大小 .
3、对于同样的距离，船在静水中来回行驶一次所花 的时间与在流水中来回行驶一次所花的时间是否相 等？请说明理由.（船在静水中的速度与在流水中的 速度一致）
探究发现
设某人下半身长为a(cm)，全身长为b(cm)，请问 这个人穿上m(cm)的高跟鞋后，下半身长与全身 长的比值会增加吗？
问：两个实数如何比较大小？
ab 0a b a b 0 a b ab 0a b
探究发现
课外小知识
古希腊维纳斯女神塑像及太阳神阿波罗塑像都通 过故意延长双腿，使之与身高的比值为0.618， 从而创造艺术美之神话.
It is important to make eye contact with your teamplayers when playing basketball.
Without hesitation, she went to Simon and gave him a big smile.
hesitation 犹豫 n.
探究发现
归纳小结 1、比较大小的一般步骤是：
作差 变形 判断符号
下结论
2、一般地，设a，b为正实数，且 a b,m 0 则有
am a bm b
探究发现
【探究2】日常生活中，还有哪些实例满足上 述结论？
例题讲解
【例1】试比较 x 1x 5与x 32的大小.
【练习1】已知0 a b，试比较 a3 b3 与 ab2 a2b 的大小 .
【例】甲、乙两人同时从A地出发沿同一路线 走到B地，甲有一半时间以速度m行走，另一 半时间以速度n行走；乙有一半路程以速度m 行走，另一半路程以速度n行走，如果m≠n.问 甲、乙两人谁先到达指定地点？
【练习】甲、乙两位采购员同去一家粮食销售 公司买了两次粮食，两次粮食的价格不同，两 位采购员的购粮方式也不同。其中，甲每次购 买1000kg，乙每次购粮用去1000元钱，谁的购 粮方式更合算？
Simon
rest head on hand, look downwards, never smile,
look unfriendly, make others go away
well-dressed 穿着讲究的adj. People are well-dressed at
the wedding.
The customers always prefer Debbie to me. prefer A (to B) 选择Ａ(而不选择 Ｂ) 你想喝什么，茶还是咖啡？
Which would you prefer, tea or coffee? 我想喝茶，不想喝咖啡．
I prefer tea to coffee. 她愿意步行，不愿意骑车．
enter 进入,登台 v.
Don’t enter the office without knocking. exit 退出,退场 v. 出口 n.
• exit visa出境签证 fire exit安全出口
entrance 入口 n.
glance at 匆匆一看
浏览报纸
glance at the newspapers greet 和某人打招呼，迎接v. greeting 问候，欢迎n.
• What kind/sort of shoes would
you like?
You whole appearance
communicates things.
你的整体外貌都能传达信息． appearance外观，外貌．出现
n. Don’t judge by appearances. 切勿以貌取人． appear 出现 v. He didn’t appear until 9pm. 直到９点他才出现．
• People in France greet friends with kissing instead of shaking hands.
sigh 叹气 v. / n.
‘How can I lose my weight?’,he sighed. Miss Cat left with a sigh.
3. Who gives Simon advice? A senior employee, Mr Young. 4. In the photo, which person looks more friendly, the boy or the girl?
The girl (Debbie).
Read the story and complete the chart:
Poor guy!
a senior employee 一位级别较高的职员 • senior: holding a higher position • employee: a person who is paid to work for other people
What’s up, Simon? What’s up? = What’s the matter?
祝各位专家身体健康、工作顺利 祝各位同学学习进步、快乐成长
Ways of communicating
Spoken
speaking
language
ringing
Written language
writing typing
Body
gesturing
language
gesture 手势，姿势 n.
remind 提醒 v.
Do I have to remind you again? 需要我再次提醒你吗？
remind sb of sth.提醒某人某事
This song reminds me of my hometown. 这首让我想起了我的家乡．
reminder提示信，通知信 n.
课堂小结
1、比较大小：
（1）步 骤：作差→变形→判断符号→下结论
（2）关键点： “变形”是作差比较大小的关键， “变形”的目的在于判断差的符号，而不必考虑 差的值是多少.“变形”的常用 方法有通分、因式 分解、配方等.
2、一般地，设a，b为正实数，且 a b,m 0
则有
am a bm b
3、应 用：灵活地应用比较大小的知识来解决
She agreed without hesitation. 她毫不犹豫地同意了．
hesitate犹豫 v.
Don’t hesitate to tell us if you have a problem.
She wanted to remind me that tomorrow is her birthday.
Speech is not the only way we
communicate. • 语言并不是我们唯一的沟通方式.
It’s the way you stand and sit. •它是你站立和坐姿的方式。 定语从句
What kind of language is that?
• 那是一种怎样的语言? • What kind/sort of…?什么类型…？
name Body language
outcome
sit up and hold head up, look friendly, Debbie make eye contact with the make others
customers, always smile, feel welcome greet cheerfully
She prefers walking to cycling.
It’s the way you communicate.
communicate with sb. 与某人沟 通
Parents should always communicate with their children.
communication沟通，交流 n. Speech is not the only method of
Simon
make eye contact with 与某人眼神交流
Debbie
She is holding her head up.
She smiles.
She makes eye contact with the customers.
make eye contact with 与某人眼神交流
He does not make a good impression on people.
make a good imopression on sb. 给某人留下好印象
He rests his head on his hand.
rest 被支撑，托v.
He doesn’t look up. He never smiles.
C Find the meaning
C1 1. d 2. f 3. a 4. c 5. e 6. b
C2 1. sighed 2. appearance 3. without hesitation 4. part-time 5. gestures 6. speech
D Read and think
【练习2】设 a x2 x ,b x 2 ，则a与
b的大小关系为（ ）.
A、a b B、 a b C、a b D、与x有关
例题讲解
归纳小结
“变形”是作差比较大小的关
键“变. 形”的目 的:
在于判断差的符号， 而不必考虑差的值是多少.
“变形” 的常用方 法:
通分、因式分解、配方等.
知识应用
探究发现
设某人下半身长为a(cm)，全身长为b(cm)，请问 这个人穿上m(cm)的高跟鞋后，下半身长与全身 长的比值会增加吗？
不等式的性质
1、若a>b，则a+c > b+c 2、若a>b，c>0，则ac > bc 3、若a>b，c<0，则ac < bc 4、若a>b，b>c，则a > c（传递性）
a Mr Young said that body language is important. 4 b The lady walked over to Debbie instead of Simon2. c Simon began to sit up and smile. 6 d A well-dressed lady entyered the travel agency. 1 e Simon’s sister came to remind hm of her birthday.7 f SImon sighed. 3
thumbs up
good job / the number one
gesture 手势，姿势 n.
OK
bad
gesture 手势，姿势 n.
Be quiet!
Come here.
expressiFra Baidu bibliotekn 表情，神态
shocked
thoughtful
expression 表情，神态
tired excited
communication. 语言并不是唯一的沟通方式．
I don’t even get a chance to speak to them.
我甚至没有和他们说话的机会．
get a chance有机会
take a chance
冒一冒险, 碰碰运气,
by chance偶然, 意外地 I met an old friend by chance.
Where’s my I won a tour It’s unfair!
Mum?
around world?
angry surprised
sad
disappointed
Why can’t I find a good job?
disappointed adj. be disappointed at sth. Jay was disappointed at the bad news.
比较大小
创设情景
大家观察右图，请问这两个人谁更漂亮？
2.8 0.51 3.8 0.58
5.5
6.5
5.5 2.8
6.5 3.8
创设情景
理论依据 一般的人，下半身长与全身长的比值，在 0.57~0.60 之间，当这个比值越接近黄金分割 值0.618时人的身材就越好.
探究发现
【探究1】为什么芭蕾舞演员在表演时，脚尖立起来 给人以美的享受？