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问题 解答题

给定两个命题，P：对任意实数x都有ax2+ax+1＞0恒成立；Q：关于x的方程x2-x+a=0有实数根；如果P与Q中有且仅有一个为真命题，求实数a的取值范围．

答案

对任意实数x都有ax2+ax+1＞0恒成立⇔a=0或

a＞0
△＜0
⇔0≤a＜4；

关于x的方程x2-x+a=0有实数根⇔1-4a≥0⇔a≤

1
4
；

如果P正确，且Q不正确，有0≤a＜4，且a＞

1
4
∴
1
4
＜a＜4；

如果Q正确，且P不正确，有a＜0或a≥4，且a≤

1
4
∴a＜0．

所以实数a的取值范围为(-∞，0)∪(

1
4
，4)．

单项选择题

A project life cycle is a collection of generally sequential project (73) whose name and number are determined by the control needs of the organization or organizations involved in the project. The life cycle provides the basic (74) for managing the project, regardless of the specific work involved.

（74）处填（）。

A．plan

B．fraction

C．main

D．framework
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选择题

At the weekend I often go to the bookshop ________ new books.

A．look at

B．to have a look at

C．look for

D．to look on
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