题目内容
已知函数
(
)
(1)若
,作出函数
的图象;
(2)设
在区间
上的最小值为
,求
的表达式.
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129721849.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129799399.png)
(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129814337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
(2)设
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129939380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130001321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130001321.png)
(1)
.
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201303292027.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201301261222.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201303292027.png)
去绝对值号时,分类讨论,
,分段画图;
在区间
上的最小值时,
,转化为定区间动轴问题,分类讨论。
解:(1)若
,则
图略.
(2)考虑
,则
(
).
若
时,
,
在区间
上是减函数,所以
的最小值
.
若
,
.
①若
,即
时,
在区间
上是增函数,所以
的最小
.
②若
,即
时,
的最小值
.
③若
,即
时,
在区间
上是减函数,所以
的最小值
.
综上得,![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201303292027.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201301261222.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129939380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130532343.png)
解:(1)若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129814337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201301261222.png)
(2)考虑
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130891510.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130922806.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129799399.png)
若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130969370.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220130984533.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129939380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131078660.png)
若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131093408.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201311091081.png)
①若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131140588.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131156486.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129939380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131312740.png)
②若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131343574.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131359609.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131390974.png)
③若
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131421521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131437542.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129939380.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220129830447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/20140823220131530774.png)
综上得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140823/201408232201303292027.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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