题目内容
设二次函数
满足
的两实数根分别为3和1,图象过点(0,3).
(1)求
的解析式;
(2)求函数
在区间
上的最大值.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302339429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302370884.png)
(1)求
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302339429.png)
(2)求函数
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302339429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302666374.png)
解:(1)
;(2)最大值为
。
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302698681.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302713507.png)
本试题主要是考查了二次函数的解析式的求解,以及二次函数在给定区间的最值问题。
(1)因为弦设出
,然后利用f(x)=0的两实数根分别为3和1,图象过点(0,3).那么得到a,b,c的关系式然后得到结论。
(2)根据上一问的解析式,求解二次函数对称轴,结合定义域得到最值。
解:(1) 设
,由题意得,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232223029001000.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222303056702.png)
(2)
的对称轴
,
的最大值为![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302713507.png)
(1)因为弦设出
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302869824.png)
(2)根据上一问的解析式,求解二次函数对称轴,结合定义域得到最值。
解:(1) 设
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302869824.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232223029001000.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222303056702.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222303072474.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222303103363.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222303119459.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823222302713507.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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