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问题 填空题
向量
a
、
b
满足（
a
-
b
）•（2
a
+
b
）=-4，且|
a
|=2，|
b
|=4，则
a
与
b
夹角的余弦值等于______．
答案

（

a
-
b
）•（2
a
+
b
）=-4，

得2

a
2-
b
2-
a
•
b
=-4

又|

a
|=2，|
b
|=4，

∴8-16-2×4cosθ=-4   （θ是

a
与
b
夹角）

∴cosθ=-

1
2

应填-

1
2
．

单项选择题

Listen carefully, working people, we would like to tell you something that could save your precious time and money! Best of all, it is free!
It’s "no".
What do you ask We’ll say it again: "No. "
Sweet and simple "no".
Say "no" at your office and see how quickly that pile of work on your desk disappears.
"Saying ’no’ to others means you are saying ’yes’ to yourself, " said Leslie Charles, a professional speaker from East Lansing, Michigan.
"Time is precious. People are spending money buying time. And yet we are willing to give up our time because we can’t say ’no’. "
Susie Watson, a famous writer, said people who always say "yes" need to say "no" without guilt or fear of punishment. "I would rather have someone give me a loving ’no’ than an obligated ’yes’, " she said.
Susie Watson says she feels "no" obligation to give an explanation when she says "no" either socially or professionally. Does she feel guilty about it "Not at all, " said Watson, who is director of advertising and public relations at Timex Corp in Middlebury, Conneticut. "Most people are afraid of saying ’no’... My advice is to say ’yes’ only if you don’t mean ’no’. "
Watson said "no" is the most effective weapon against wasting time. "Every year there are more demands on your time... Other people are happy to use up your time, " Watson said. Time saving appears to be "no’s" greatest friend.
"No" can be your new friend, a powerful tool to take back your life. "No" may even take you further in the business world than "yes".
"No" is power and strength. "No" now seems completely correct. "Saying ’no’ isn’t easy. But finally it’s greatly liberating, " Charles said. But, he added, "a ’no’ project needs to be worked on every day because it is hard to change long-term habit. "
But, he also warns: "Don’t go to extremes. Don’t find yourself saying ’no’ to everything. In return you should learn to hear ’no’. \

When you say "no" to others you should say it in a ______.

A. secret way


B. polite way
C. proud way


D. guilty way
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单项选择题

阳江拥有中国最大的（）生产基地。

①毛毯

②果冻布丁

③鱼翅

④刀具

⑤珍珠

A.③④⑤

B.②③④

C.①②④

D.①②⑤
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