【题文】已知函数,且,,(1)试问是否存在实数,使得在上为减函数,并且在上为增函数,若不存在,说明理由. (2)当时,求的最小值.
题型:难度:来源:
【题文】已知函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212518-40986.png)
,且
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212518-52231.png)
,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-92239.png)
,
(1)试问是否存在实数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-62822.png)
,使得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-85184.png)
在
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212520-55498.png)
上为减函数,并且在
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212520-38547.png)
上为增函数,若不存在,说明理由.
(2)当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212520-65497.png)
时,求
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-85184.png)
的最小值
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212521-53238.png)
.
答案
【答案】(1)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212521-97226.png)
; (2)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212522-33552.png)
.
解析
【解析】
试题分析:(1)由题意求得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212523-26669.png)
的解析式,可得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-92239.png)
的解析式,设
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212523-61189.png)
,求得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212523-35748.png)
(x1+x2)(x1?x2)[x12+x22+(2?λ)].根据题意得,当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212524-27377.png)
时,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212524-37518.png)
,求得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212525-38859.png)
.当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212526-84093.png)
时,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212526-32858.png)
,求得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212526-24072.png)
,综合可得λ的值.
(2)由于
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212527-86878.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212527-56195.png)
,当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212528-65227.png)
时,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212528-63710.png)
,分类讨论,求得
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212527-86878.png)
的最小值
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212528-85876.png)
.
试题解析:
(1)由题意可得:
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212529-28044.png)
.
所以
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212529-73034.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212530-11376.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212530-79066.png)
,
由题设当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212524-27377.png)
时, 所以
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212531-52586.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212531-11912.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212532-20053.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212533-94817.png)
所以当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212524-27377.png)
时,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212533-94151.png)
,且
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212534-72875.png)
,
又因为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-85184.png)
在
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212520-55498.png)
上为减函数,所以
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212534-80001.png)
;
当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212526-84093.png)
时,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212534-49649.png)
,且
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212535-11423.png)
,
又因为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212519-85184.png)
在
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212520-38547.png)
上为减函数,所以
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212535-45499.png)
故
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212521-97226.png)
.
根据题意可得:
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212529-73034.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212530-11376.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212530-79066.png)
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212535-92887.png)
当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212536-98649.png)
时,即
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212536-69052.png)
时,最小值
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212536-19557.png)
;
当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212537-59838.png)
时,即
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212537-94800.png)
时,最小值为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212538-36934.png)
;
当
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212538-87356.png)
时,即
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212539-33660.png)
时,最小值为为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212539-21027.png)
.
所以综上可得:
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212522-33552.png)
.
考点:函数性质的综合应用.
举一反三
【题文】对
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212510-32967.png)
,记
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212511-79916.png)
,按如下方式定义函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212511-42879.png)
:对于每个实数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212511-53713.png)
,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212511-56623.png)
.则函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212511-42879.png)
最大值为
________________ .
【题文】定义在R上的函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212439-25568.png)
为奇函数,对于下列命题:
①函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212439-43169.png)
满足
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212440-97516.png)
; ②函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212439-43169.png)
图象关于点(1,0)对称;
③函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212440-45583.png)
的图象关于直线
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212441-94364.png)
对称; ④函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212440-45583.png)
的最大值为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212441-18811.png)
;
⑤
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212442-97985.png)
.其中正确的序号为________.
【题文】已知函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212418-14337.png)
是定义在
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212418-39680.png)
上的奇函数,且
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212418-88059.png)
,若
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212419-24916.png)
,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212419-34767.png)
,则有
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212419-95806.png)
.
(1)判断
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212418-14337.png)
的单调性,并加以证明;
(2)解不等式
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212420-70747.png)
;
(3)若
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212420-82539.png)
对所有
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212421-99280.png)
,
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212421-85757.png)
恒成立,求实数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212421-75244.png)
的取值范围.
【题文】已知
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212349-31133.png)
为
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212349-40435.png)
上增函数,且对任意
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212350-35882.png)
,都有
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212350-71981.png)
,则
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212351-43615.png)
____________.
【题文】设关于
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212300-69555.png)
的方程
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212300-45452.png)
有两个实根
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212301-27086.png)
,函数
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212301-34833.png)
.
(1)求
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212302-32871.png)
的值;
(2)判断
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212303-66410.png)
在区间
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212303-29450.png)
的单调性,并加以证明;
(3)若
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212304-20591.png)
均为正实数,证明:
![](http://img.shitiku.com.cn/uploads/allimg/20200325/20200325212304-20883.png)
最新试题
热门考点