最新高二数学暑假预科讲义 第十一讲 导数初步 中等学生版
目录
第十一讲 导数的概念与运算 (2)
考点1:导数的定义 (2)
题型一:求平均变化与瞬时变化率 (2)
考点2:导数的运算 (5)
题型二:导数运算 (5)
题型三:()f a '实际是一个数 (8)
课后综合巩固练习 (9)
第十一讲 导数的概念与运算
考点1:导数的定义
1.函数的平均变化率:
一般地,已知函数()y f x =,0x ,1x 是其定义域内不同的两点,记10x x x ?=-, 10y y y ?=-10()()f x f x =-00()()f x x f x =+?-,
则当0x ?≠时,商
00()()f x x f x y
+?-?=
称作函数()y f x =在区间[,]x x x +?(或00[,]x x x +?)上的平均变化率.
2.函数的瞬时变化率、函数的导数:
设函数()y f x =在0x 附近有定义,当自变量在0x x =附近改变量为x ?时,函数值相应的改变00()()y f x x f x ?=+?-. 如果当x ?趋近于0时,平均变化率
00()()
f x x f x y x x
+?-?=
??趋近于一个常数,那么常数称为函数()f x 在点0x 的瞬时变化率. “当x ?趋近于零时,00()()
f x x f x x
+?-?趋近于常数l ”可以用符号“→”记作:
“当0x ?→时,
00()()f x x f x l x +?-→?”,或记作“000()()
lim x f x x f x l x
?→+?-=?”,符号
“→”读作“趋近于”.
函数在0x 的瞬时变化率,通常称为()f x 在0x x =处的导数,并记作0()f x '. 这时又称()f x 在0x x =处是可导的.于是上述变化过程,可以记作 “当0x ?→时,000()()()f x x f x f x x +?-'→?”或“0000()()
lim ()x f x x f x f x x
?→+?-'=?”.
题型一:求平均变化与瞬时变化率
例1.(1)(2018春?道里区校级月考)已知一质点的运动方程为22s t =-,则该质点在一段时间[0,2]内的平均速度为 .
(2)(2019春?武昌区校级期中)函数2()3f x x =在[2,6]内的平均变化率为 .
(3)(2019春?思南县校级月考)一物体作直线运动,其运动方程为2()2s t t t =-+,则
1t =时其速度为 .
(4)(2018秋?广陵区校级期中)若某物体运动规律是3265(0)S t t t =-+>,则在t = 时的瞬时速度为0.
例2.(1)求下列函数在区间00[]x x x +?,上的平均变化率.
① ()f x x = ② 2()f x x = ③ 3()f x x = ④1
()f x x
= ⑤()f x =
(2)求下列函数分别在1x =,2x =和3x =处的瞬时变化率.
① ()f x x = ② 2()f x x = ③ 3()f x x = ④ 1
()f x x
= ⑤ ()f x =
例3.已知()()40f x kx k =+≠,且()f x 在区间[]12-,上的平均变化率是4,则k =____.
例4.(1)(2017春?揭东区校级月考)已知1()f x x =,则0lim x → (2)(2)
f x f x
+-的值
是 .
(2)(2018春?西城区校级期中)已知函数2()f x x =,则0
(1)(1)
lim x f x f x
→+-= .
(3)(2018春?孝感期末)已知()f x xlnx =,求0
(32)(3)
lim x f x f x
→+-=
(4)(2017秋?临夏市校级期末)设函数()f x 在1x =处存在导数为2,则
(1)(1)
lim 3x f x f x
→+-= .
(5)(2017春?永昌县校级月考)设函数()f x 可导,f '(1)1=则
(1)(1)
lim 3x f x f x
→+-= .
(6)(2018春?咸阳期末)若()y f x =在(,)-∞+∞上可导,且0
(2)()
lim 13x f a x f a x
→+-=,
则f '(a )= .
考点2:导数的运算
1.可导与导函数:
如果()f x 在开区间(,)a b 内每一点都是可导的,则称()f x 在区间(,)a b 可导.这样,对开区间(,)a b 内每个值x ,都对应一个确定的导数()f x '.于是,在区间(,)a b 内,()f x '构成一个新的函数,我们把这个函数称为函数()y f x =的导函数.记为()f x '或y '(或x y '). 导函数通常简称为导数.如果不特别指明求某一点的导数,那么求导数指的就是求导函数.
2.基本初等函数的导数公式
(1)若()f x C =(C 为常数),则()0f x '=; (2)若()()f x x αα*=∈Q ,则()1f x x αα-'=;
(3)若()x f x a =,则()ln x f x a a '=;特别地, 若()e x f x =,则()e x f x '=; (4)若()log a f x x =,则()1ln f x x a '=
;特别地,若()ln f x x =,则()1
f x x
'=; (5)若()sin f x x =,则()cos f x x '=; (6)若()cos f x x =,则()sin f x x '=-.
3.导数的四则运算法则:其中()()f x g x ,
都是可导函数,C 为常数: (()())()()f x g x f x g x '''±=±;[()()]()()()()f x g x f x g x f x g x '''=+; [()]()Cf x Cf x ''=;2
()()()()()
()()f x f x g x f x g x g x g x '''??-=????
(()0g x ≠).
题型二:导数运算
例5.(1) 求下列函数的导数
①2012y x = ②2x y = ③e x y = ④ln y x =
(2)求下列函数的导数
①3cos y x x =+ ②()
231e x y x x =-+ ③e sin x y x = ④ln x
y x
=
⑤()tan f x x =
(3)求下列函数的导数
① ()2
211f x x x x x ?
?=++ ??
? ② )
11y ?=
??
③()sin cos 22x x
f x x =-
例6.(1)313y x =;(2)21
y x =;(3)42356y x x x =--+;(4)2cos y x x =+;(5)
2sin y x x =+;(6)sin cos y x x =-;(7)1y x x
=+
;(8)1
y x =(9)e x y x =;
(10)sin y x x =;(11)2ln y x x =;(12)cos sin y x x x =-;(13)1
21
y x =
+;(14)
2
1x y x =
+;(15)11x y x -=+;(16)sin x y x
=;(17)()2
2πy x =;(18))
2
2y =;
(19)()
()22331y x x =+-;(20)()()
211y x x x =+-+.
例7.(1)(2019春?龙凤区校级期中)已知函数()f x
=
的导数为()f x ',则f '(4)(=
)
A .18
B .18
-
C .
116
D .116
-
(2)(2019春?香坊区校级期中)设()f x lnx =,若0()3f x '=,则0(x = ) A .3e
B .3
C .1
3
D .3ln
(3)(2019春?玉山县校级期中)设()f x '是函数cos ()x x
f x x e
=+的导函数,则(0)f '的值为( )
A .1e
B .1-
C .0
D .2
(4)(2019春?诸暨市校级期中)已知()x f x e lnx =-,则f '(1)(= ) A .e B .1e - C .0
D .1
1e
-
(5)(2019春?宁德期中)已知1()cos f x x =,21()()f x f x '=,32()()f x f x =',43()()f x f x =',?,1()()n n f x f x -=',则2019()f x 等于( )
A .sin x
B .sin x -
C .cos x
D .cos x -
(6)(2019春?莱西市校级月考)设0()sin f x x =,10()()f x f x '=,21()()f x f x '=,?,1()()n n f x f x '+=,n N ∈,则2020()f x 等于( )
A .sin x
B .sin - x
C .cos x
D .cos - x
题型三:()f a '实际是一个数
例8.(1)已知()()3
3215f x x f x '=--+,则()2f '-=______
(2)(2019春?历下区校级期中)已知21
()2(2019)20192f x x xf lnx '=-+-,则(1)f '(=
) A .2017 B .2018
C .2019
D .2020