“已知函数 f(x)=x2+ax+a(a∈R) ，求证： |f(1)| 与 |f(2)| 中至少有一个不小于 12 。”用反证法证明这个命题时，下列假设正确的是( )

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“已知函数 f(x)=x2+ax+a(a∈R) ，求证： |f(1)| 与 |f(2)| 中至少有一个不小于

1

2

。”用反证法证明这个命题时，下列假设正确的是( )

A：假设 $| f (1) | \geq \frac{1}{2}$ 且 $| f (2) | \geq \frac{1}{2}$ ;

B：假设 $| f (1) | < \frac{1}{2}$ 且 $| f (2) | < \frac{1}{2}$ ;

C：假设 $| f (1) |$ 与 $| f (2) |$ 中至多有一个不小于 $\frac{1}{2}$ ;

D：假设 $| f (1) |$ 与 $| f (2) |$ 中至少有一个不大于 $\frac{1}{2}$ .

上一题下一题 0.0难度选择题更新时间:2019-01-25 05:09:06

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B

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根据短文内容及首字母提示，填写所缺单词，使短文意思完整。每空一词。
The environment is becoming worse and worse . There are many kinds of pollution that I worry a____ . The most serious two are n____ pollution and air pollution , because people can't live h____ with polluted air. Animals can't live in the world , e____ . More and more people are becoming i____ because of polluted air .
I think factories should not p____ dirty water into rivers directly. We'd better go on foot or by bike i____ of by car . Finally , everyone must pay a____ to rubbish pollution . If everyone makes so much rubbish , one day we may live in a world f____ of rubbish . How terrible it will be ! We should take a____ to make our world cleaner and more beautiful

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