题目
题型:单选题难度:一般来源:不详
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060738-27555.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060738-12406.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-60502.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-60102.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-86182.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-29730.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-13149.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060740-23734.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060740-34368.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060740-20401.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060740-35381.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060740-50475.png)
答案
解析
分析:由于二次函数f(x)=ax2-4x+c的值域为[0,+∞),所以a>0,且△=0,从而得到a,c的关系等式,再利用a,c的关系等式解出a,把
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-60102.png)
解:因为二次函数f(x)=ax2-4x+c的值域为[0,+∞),
所以
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060741-59069.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060741-44422.png)
所以
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060739-60102.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060741-90408.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060741-72114.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060741-54714.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060742-22339.png)
由于a+
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060742-10864.png)
所以1+
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060742-22339.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060742-94653.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060742-14618.png)
故答案为:C
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060736-77772.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060736-74683.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060736-40772.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060732-64810.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-35142.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-87159.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-33439.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-18058.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-23958.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060733-85385.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060734-71357.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060728-85033.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060729-97876.png)
A.5 | B.4 | C.8 | D.6 |
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060725-56202.gif)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060721-11134.png)
![](http://img.shitiku.com.cn/uploads/allimg/20190818/20190818060721-22358.png)
A.4 | B.-4 | C.2 | D.-2 |
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