题目内容
对于函数
,当实数
属于下列选项中的哪一个区间时,才能确保一定存在实数对
(
),使得当函数
的定义域为
时,其值域也恰好是
( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446885697.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446901312.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446917396.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446932490.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446948447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446963432.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022446979438.png)
A.![]() | B.![]() | C.![]() | D.![]() |
D
试题分析:函数f(x)=-3x3+k的图象开口向下,对称轴为y轴,若存在实数对a,b(a<b<0),使得当函数f(x)的定义域为[a,b]时,其值域也恰好是[a,b],从而-3a2+k=a,-3b2+k=b,所以方程3t2+t-k=0有两个不等的负根a,b,
∴△=1+12k>0且a+b=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022447057351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022447073431.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824022447088623.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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