含参的函数单调区讨论典例(二).pdf
《含参的函数单调区讨论典例(二).pdf》由会员分享,可在线阅读,更多相关《含参的函数单调区讨论典例(二).pdf(8页珍藏版)》请在淘文阁 - 分享文档赚钱的网站上搜索。
1、1 导数应用:含参函数的单调性讨论(二)对函数(可求导函数)的单调性讨论可归结为对相应导函数在何处正何处负的讨论,若有多个讨论点时,要注意讨论层次与顺序,一般先根据参数对导函数类型进行分类,从简单到复杂。一、典型例题例 1、已知函数32()331,f xaxxxaR,讨论函数)(xf的单调性.分析:讨论单调性就是确定函数在何区间上单调递增,在何区间单调递减。而确定函数的增区间就是确定0)(xf的解区间;确定函数的减区间就是确定0)(xf的解区间;讨论单调性与讨论不等式的解区间相应。解:因为32()331,f xaxxxaR,所以/2()3(21)fxaxx (1)当0a时,/()3(21)fx
2、x,当1,2x时,/()0fx;当1,2x时,/()0fx;所以函数()f x在1(,2上单调递增,在1,)2上单调递减;(2)当0a时,/2()3(21)fxaxx的图像开口向上,36(1)aI)当136(1)0,aa时,时,/()0fx,所以函数()f x在 R上递增;II)当0136(1)0,aa时,时,方程/()0fx的两个根分别为121111,aaxxaa且12,xx所以函数()f x在11(,)aa,11(,)aa上单调递增,在1111(,)aaaa上单调递减;(3)当0a时,/2()3(21)fxaxx的图像开口向下,且36(1)0a方程/()0fx的两个根分别为121111,a
3、axxaa且12,xx所以函数()fx在11(,)aa,11(,)aa上单调递减,在1111(,)aaaa上单调递增。2 综上所述,当0a时,所以函数()f x在1111(,)aaaa上单调递增,在11(,)aa,11(,)aa上单调递减;当0a时,()f x在1(,2上单调递增,在1,)2上单调递减;当01a时,所以函数()f x在11(,)aa,11(,)aa上单调递增,在1111(,)aaaa上单调递减;当1a时,函数()f x在 R上递增;小结:导函数为二次型的一股先根据二次项系数分三种情况讨论(先讨论其为0 情形),然后讨论判别式(先讨论判别式为负或为0 的情形,对应导函数只有一种符
4、号,原函数在定义域上为单调的),判别式为正的情况下还要确定两根的大小(若不能确定的要进行一步讨论),最后根据导函数正负确定原函数相应单调性,记得写出综述结论。例 2(2010 山东理数改编)已知函数1()ln1afxxaxx()aR.讨论()f x的单调性;解:因为1()ln1af xxaxx的定义域为),0(所以222111()(0,)aaxxafxaxxxx,令2()1,(0,)h xaxxa x,则)()(xgxf与同号法一:根据熟知二次函数性质可知g(x)的正负符号与开口有关,因此可先分类型讨论:文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码
5、:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6
6、HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 Z
7、G10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档
8、编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O
9、6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9
10、 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7
11、文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R73 当0a时,由于110a1,)(xh开口向下,结合其图象易知(0,1)x,()0h x,此时()0fx,函数()f x单调递减;(1,)x时,()0h x,此时()0fx,函数()f x单调递增.当0a时,)(xh开口向上,但2x是否在定义域需要讨论:因10011aaa或所以i)当1a时,由于110a1,)(xh开口向上,结合其图象易知(0,1)x,
12、()0h x,此时()0fx,函数()f x单调递增.(1,)x时,()0h x,此时()0fx,函数()f x单调递减;ii)当10a时,g(x)开口向上且),0(,21xx,但两根大小需要讨论:a)当12a时,12,()0 xxhx 恒成立,此时()0fx,函数()fx在(0,+)上单调递减;b)当1101 102aa 时,g(x)开口向上且在(0,)有两根(0,1)x时,()0h x,此时()0fx,函数()f x单调递减;1(1,1)xa时()0h x,此时()0fx,函数()fx单调递增;1(1,)xa时,()0h x,此时()0fx,函数()f x单调递减;c)当121a时,111
13、0a,g(x)开口向上且在(0,)有两根)11,0(ax时,()0h x,此时()0fx,函数()f x单调递减;)1,11(ax时()0h x,此时()0fx,函数()fx单调递增;),1(x时,()0h x,此时()0fx,函数()f x单调递减;小结:此法是把单调区间讨论化归为导函数符号讨论,而确定导函数符号的分子是常见二次型的,一般要先讨论二次项系数,确定类型及开口;然后由于定义域限制讨论其根是否在定义域内,再讨论两根大小注,结合g(x)的图象确定其在相应区间的符号,得出导函数符号。讨论要点与解含参不等式的讨论相应。文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9
14、A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM
15、7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9
16、L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10
17、A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:
18、CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 H
19、I9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG
20、10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R74 法二:10011aaa或i)当0a时,由于110a1,)(xh开口向下,结合其图象易知(0,1)x,()0h x,此时()0fx,函数()f x单调递减;(1,)x时,()0h x,此时()0fx,函数()f x单调递增.ii)当1a时,由于11 0a0)令2()2(1)2(1)1g xaa xa x,则)(xf与)(xg同号(
21、1)当1a时,xxfxxfxgln)(,01)(,1)(在定义域),0(上为增函数(2)当1a时,224(1)8(1)121644(31)(1)aaaaaaa当0113a时,g(x)开口向上,图象在x 轴上方,所以0)(xg所以()0fx,则()f x在(0,)上单调递增当0131aa或,此时令()0fx,解得)1(21,)1(2121aaaxaaax由于210)(100)1(2xxxgaaa开口向上且,因此可进一步分类讨论如下:i)当1a时,120)(0)1(2x,xxgaa开口向下文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3
22、O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S9 ZG10A9A2R9R7文档编码:CM7Y5O4S3O6 HI9L6U4T2S
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 函数 单调 讨论
限制150内