重难点04 利用导数研究不等式恒(能)成立问题【七大题型】
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ð 1'2024·¤ñòóÃôõ·ö÷)
e𝑥−e
𝑎≥e + ln𝑎𝑥𝑥∈(0, + ∞)&*+MA𝑎;md' )
Axe2−e
2
Bx2e
1
2−e
Cxe1−e
Dxe1+1
e−e
C% 1-1'2024·øùúû·÷üýþ)ÿt#$%ln𝑥−
2
𝑥−𝑎−1
e
1
𝑥2 +
e ≤0:¬
!MA¬
𝑎;Ā
12d' )
Ax −∞,−1
2e
Bx(−∞,0)
Cx −1
2e , + ∞
Dx[0, + ∞)
C% 1-2'2024·āĂ*ă·÷üýþ)·𝑥;#$%(e−1)(ln𝑎+ 𝑥) ≥𝑎e𝑥−1𝑥∈[0,1]¤:!MA¬
𝑎;Ā12J' )
Ax 1
2e ,e2
Bx 1
e ,e
Cx 1
e ,e2
Dx 1
2e ,e
C% 1-3'2024·ĄąĆć·Ý÷)ÿt8
𝑓(𝑥) =
1
e𝑥+1−𝑥3M·ĈU;𝑥∈(1,2]M#$%𝑓𝑥+1
𝑥−1 +𝑓
𝑡+1
(𝑥−1)2(𝑥−6) < 1&*+MA¬
𝑡;Ā12d' )
Ax(1, + ∞)
Bx[−1,1]
Cx(−∞,−1]
Dx(−∞,−1)
2 -./
0/
12
ð 2'2024·ĉĊċĂ·÷üýþ)ÿt𝑎∈𝑁∗M8
𝑓(𝑥) = e3𝑥−𝑥𝑎> 0&*+MA𝑎;md' )
Ax2
Bx3
Cx6
Dx7
C% 2-1'2024·āĂČč·ö÷)ÿt#$%𝑎𝑥e𝑥+𝑥> 1−ln𝑥:!MA¬
𝑎;Ā12d'ĎĎ)
Ax −1
e2 , + ∞
Bx −1
e , + ∞
Cx −∞, 1
e2
Dx −∞, 1
e
C% 2-2'2024·āĂ*ă·Ý÷)𝑥∈[0, + ∞)M𝑥2 +𝑎𝑥+ 1 ≤e𝑥&*+MA¬
𝑎;md' )
Ax𝑒
Bx2
Cx𝑒−1
Dx𝑒−2
C% 2-3'2024·āĂďĐ·Ý÷)ÿt8
𝑓(𝑥) =
1
3𝑥3M𝑔(𝑥) = e𝑥−
1
2𝑥2−𝑥M∃𝑥1M𝑥2 ∈[1,2]Â
|𝑔(𝑥1)−𝑔(𝑥2)| > 𝑘|𝑓(𝑥1)−𝑓(𝑥2)|'𝑘dK
)*+MAK
𝑘;Ā12d' )
Ax(−∞,e−2]
Bx(−∞,e−2)
Cx −∞, e2−3
4
Dx −∞, e2−3
4
3 -345 0/
12
ð 3'2024·đĒēĔ·Ý÷)ÿt8
𝑓(𝑥) = ln𝑥−𝑎𝑥,𝑔(𝑥) =
2
𝑎𝑥,𝑎≠0x
(1)08
𝑓(𝑥);ĕ˹º
(2)𝑓(𝑥) ≤𝑔(𝑥)&*+M0𝑎;ėx
C% 3-1'2024·āĂĘć·ö÷)ÿt8
𝑓(𝑥) = 2𝑥3−𝑎𝑥2 +2(𝑎> 0)x
(1)0ęĚ𝑦= 𝑓(𝑥)L(0,𝑓(0))¿;ěĚWX
(2)∃𝑥∈[−1,1]M|𝑓(𝑥)| ≥3M0¬
a ;Ā12x
C% 3-2'2024·Ĝĝ·Ý÷)ÿt8
𝑓(𝑥) = ln(𝑥+ 1) +𝑘(𝑥+ 1)x
(1)0𝑓(𝑥);ĕ˹º
(2)𝑓(𝑥) ≤−1&*+M0¬
𝑘;Ā12
(3)0<
𝑛
𝑖=2
ln𝑖
𝑖+1 <
𝑛(𝑛−1)
4
x'𝑛∈𝑁Ê𝑛≥2)
C% 3-3'2024·āĂ·÷üýþ)ÿt8
𝑓(𝑥) = 𝑎𝑥ln𝑥−2𝑥+ 𝑏'𝑎M𝑏∈𝑅)L(1,𝑓(1))¿;ěĚWX
d𝑦= −𝑥x
(1)08
𝑓(𝑥);Ô
(2)Ğ𝑔(𝑥) = e𝑥𝑥𝑓1
𝑥+ 2 +𝑚𝑥'𝑚∈𝑅)M𝑔(𝑥) ≥0&*+M0𝑚;Ā12x
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ð 4'2024·āĂğĠ·ö÷)ġ𝑥0 ∈[−1,2]MÂ#$%𝑥0 + (e2−1)ln𝑎≥
2𝑎
e𝑥0 + e2𝑥0−2*+MA𝑎;
Ā12J' )
Ax 1
2e ,e2
Bx 1
e2 ,e2
Cx 1
e2 ,e4
Dx 1
e ,e4
C% 4-1'2024·ĄąĆć·ö÷)· x ;#$%e𝑥+𝑥+ 2ln
1
𝑥≥𝑚𝑥2 + ln𝑚&*+MA¬
m ;m
d' )
Ax
1
2
Bxe2
4
Cxe2
2
Dxe2
C% 4-2'2023·ĢďģĤ·÷üýþ)ġ𝑥∈[1, + ∞)M·𝑥;#$% 1 + 1
𝑥
𝑥+𝑎
≥e*+MA
¬
𝑎;ėd' )
Ax2
Bx
1
ln2
Cxln2−1
Dx
1
ln2−1
C% 4-3'2024·ĥùĦć·ö÷)ÿt8
𝑓(𝑥) = e𝑘𝑥+1M𝑔(𝑥) = 1 + 1
𝑥ln𝑥.𝑘𝑓(𝑥) ≥𝑔(𝑥)MA k ;Ā
12d' )
Ax(0,e]
Bx[e,+∞)
Cx 1
e , + ∞
Dx 0, 1
e
5 9#$%&'()*+:;<=,
ð 5'2024·ħďĨ=·Ý÷)ÿt8
𝑓(𝑥) = e𝑥−sin𝑎𝑥
(1)Ü𝑎= −1nM<=
ĈU𝑥∈−π
6 , + ∞M𝑓(𝑥) > 0
(2)𝑥= 0J8
𝑓(𝑥);ÔLM0¬
𝑎;x
C% 5-1'2024·ĩĪ·÷üýþ)ÿt8
𝑓(𝑥) = e𝑎𝑥+
1
2𝑥2−𝑎𝑥'𝑎∈R).
(1)Ü𝑎= 1nM0𝑓(𝑥);
(2)Ü𝑎∈[−1,1]nM<=
ĈU;𝑥1M𝑥2 ∈[−2,2]Mă:|𝑓(𝑥1)−𝑓(𝑥2)| ≤e2−1.
C% 5-2'2024·øùīĬ·÷üýþ)ÿt8
𝑓(𝑥) = 𝑎e𝑥(𝑎≠0),𝑔(𝑥) = 𝑥2,𝑔′(𝑥)d𝑔(𝑥);G8
.
(1)<=
Ü𝑎= 1nM∀𝑥∈(0, + ∞),𝑓(𝑥) > 𝑔′(𝑥)
(2)𝑓(𝑥)9𝑔(𝑥):z²ěĚM0 a ;Ā12.
C% 5-3'2024·ĭćĮįİ·Ý÷)8
𝑓(𝑥)[𝑎,𝑏]:©VMÊ·ĈU#ı;𝑥1,𝑥2 ∈[𝑎,𝑏]Mă:
|𝑓(𝑥1)−𝑓(𝑥2)| < 𝑘|𝑥1−𝑥2|MAá𝑓(𝑥)d[𝑎,𝑏];“k 38
”
(1)𝑓(𝑥) = 𝑥2M𝑓(𝑥)Jd[1,2];“4 38
”
(2)𝑓(𝑥) =
2
eln𝑥+ (𝑎+ 1)𝑥+
1
𝑥d[1,e];“2 38
”M0¬
a ;Ā12
(3)𝑓(𝑥)d[1,2];“2 38
”Ê𝑓(1) = 𝑓(2)M<=
∀𝑥1M𝑥2 ∈[1,2]M|𝑓(𝑥1)−𝑓(𝑥2)| < 1.
6 >?@ A
ð 6'23-24 öÄ·IJij·Ĵĵ)#$%sin𝑥> 𝑥−𝑎𝑥3·𝑥∈(0,
𝜋
2)&*+M0𝑎;Ā12.
C% 6-1'2023 Ý·IJij·Ķķ)ÿt8
𝑓(𝑥)=𝑎ln𝑥+ 𝑏𝑥(𝑎,𝑏∈𝑅)𝑥=
1
2¿ĀÔMÊęĚ
𝑦= 𝑓(𝑥)L(1,𝑓(1))¿;ěĚ9Ě𝑥−𝑦+ 1 = 0ĸ.
(1)0¬
𝑎,𝑏;
(2)∀𝑥∈[1 , +∞)M#$%𝑓(𝑥) ≤(𝑚−2)𝑥−
𝑚
𝑥&*+M0¬
𝑚;Ā12.
C% 6-2'2024·Ĺĥ·ö÷)①ĺ-PM0ÔÕ:a{»o;
Ļļ——>?@ AM AP:
Ľ5
8
𝑓(𝑥)M𝑔(𝑥);G8
-ľd𝑓′(𝑥)M𝑔′(𝑥)MÊlim
𝑥→𝑎𝑓(𝑥) = lim
𝑥→𝑎𝑔(𝑥) = 0MA
lim
𝑥→𝑎
𝑓(𝑥)
𝑔(𝑥) = lim
𝑥→𝑎
𝑓′(𝑥)
𝑔′(𝑥).
②Ğ𝑎> 0Mk Jm· 1 ;ªĿ
M8
𝑓(𝑥)
ĈU𝑥∈[0,𝑎]Mŀ:𝑓(𝑥) ≥𝑓𝑥
𝑘*+MÊlim
𝑥→0𝑓(𝑥)
= 0MAá8
𝑓(𝑥)d¹º[0,𝑎]; k ŁłŃńŅ8
.
Ľ]ÀzņMŇňÄÅ,
(1)i𝑓(𝑥) = 𝑥3−3𝑥Jd¹º[0,3]; 2 ŁłŃńŅ8
(2)ʼnŊ
lim
𝑥→0(1 + 𝑥)
1
𝑥
(3)<=
sin𝑥
𝑥−π
3
< cos𝑥M𝑥∈π, 3
2 π .
C% 6-3'23-24 öÄ·đĒŋĪ·Ĵĵ)Ōō8
,nMŎŏQKŐ08
¸¹ºÉ;
,Mő8
¹º
LŒœŔŕ:UV;ŖŗMnŎŏߦÀ8
àL¿;ÔÕ®ŘřLŚś
;ŜŝMä
¹º;É.0ÔÕŎŏ:ë{W MOP:a{Ş-şĕÊŔ;W ——>
?@ A
ř AŠd
“Ğ8
𝑓(𝑥)M𝑔(𝑥)ÄŲ³
①lim
𝑥→𝑎𝑓(𝑥) = 0Mlim
𝑥→𝑎𝑔(𝑥) = 0
②L a ¿8
𝑓(𝑥)Ã𝑔(𝑥);šŢJéêÊţŤ;M¥8
𝑓(𝑥)Ã𝑔(𝑥)L a ¿ġG
③lim
𝑥→𝑎
𝑓′(𝑥)
𝑔′(𝑥) = 𝐴MOP A J¸ť©¬
Alim
𝑥→𝑎
𝑓(𝑥)
𝑔(𝑥) = lim
𝑥→𝑎
𝑓′(𝑥)
𝑔′(𝑥) = 𝐴.”
ÌÍMŦĞ:8
𝑓(𝑥) = e𝑥M𝑔(𝑥) = 𝑡𝑥+ 1.
(1)𝑓(𝑥) ≥𝑔(𝑥)&*+M0 t ;Ā12
(2)<=
e𝑥−ln𝑥≥2.
7 BCD;&'()*+,
ð 7'2023·āĂĘć·a÷)ÿt8
𝑓(𝑥) = 𝑎𝑥+ 1−𝑥ln𝑥;šŢ𝑥= 1¿;ěĚ9Ě𝑥−𝑦= 0ŧx
(1)08
𝑓(𝑥);ĕ˹º
(2)∀𝑥1,𝑥2 ∈(0, + ∞)MÊ𝑥1 > 𝑥2nM𝑓(𝑥1)−𝑓(𝑥2) > 𝑚𝑥2
1−𝑥2
2 M0¬
m ;Ā12x
C% 7-1'2023·āĂŨũ·ö÷)ÿt8
𝑓(𝑥) = 𝑎e𝑥−𝑥2:zÔL𝑥1E𝑥2.
(1)0𝑎;Ā12
(2)𝑥2 ≥3𝑥1nM#$%𝑥1 +𝜆𝑥2 ≥2𝑥1𝑥2&*+M0𝜆;ė.
C% 7-2'2024·IJij·ö÷)ÿt8
𝑓(𝑥) = 𝑥ln𝑥−
𝑎
2𝑥2−𝑥+ 𝑎(𝑎∈R)M𝑓′(𝑥)d𝑓(𝑥);G8
x
(1)Ü𝑎=
1
2nM𝑔(𝑥) = 𝑓′(𝑥)[[𝑡,𝑡+ 1](𝑡> 0);mdℎ(𝑡)M0ℎ(𝑡)
(2)ÿt𝑥1,𝑥2J8
f'x);zÔLMÊ𝑥1 < 𝑥2M#$%e1+𝑚< 𝑥1𝑥𝑚
2 &*+M0ª
m ;Ā12x
C% 7-3'2023·Ģď·ö÷)ÿt8
𝑓(𝑥) =
1
2𝑚𝑥2 + (𝑚−1)𝑥−ln𝑥(𝑚∈R)M𝑔(𝑥) = 𝑥2−
1
2e𝑥+1.
(1)45𝑓(𝑥);ĕĖ~
(2)Ü𝑚> 0nM·ĈU;𝑥1 ∈(0, + ∞)MŪġ𝑥2 ∈[1, + ∞)MÂ𝑓(𝑥1) ≥𝑔(𝑥2)M0𝑚;Ā12.
aEĕ
1x'2024·øù·÷üýþ)Ü𝑥> 0nM𝑥2 ⋅e4𝑥−2ln𝑥≥𝑎𝑥+ 1&*+MA¬
𝑎md' )
Ax
4
e
Bx4
Cx
4
e2
Dx8
2x'2024·øùīĬ·÷üýþ)ġ𝑥∈(0, + ∞)MÂ#$%𝑎2𝑥4 +𝑥≥e𝑎𝑥2 + ln2𝑥*+MA¬
𝑎;Ā
12d' )
Ax 1
2e , + ∞
Bx 1
e , + ∞
Cx −∞, 1
e
Dx −∞, 1
2e
3x'2024·Ģď·÷üýþ)ÿt𝜆> 0MĈU;𝑥> 1M#$%e2𝜆𝑥−lne
1
2𝜆ln𝑥≥0&*+MA¬
𝜆;Ā
12d' )
Ax 1
e , + ∞
Bx 1
2e , + ∞
Cx[2e, + ∞)
Dx[e, + ∞)
4x'2024·đĒū·÷üýþ)ÿt8
𝑓(𝑥) = 𝑎𝑒𝑥+1n
𝑎
𝑥+2−2M𝑓(𝑥) > 0&*+MAª¬
𝑎;Ā12
J' )
Ax0 < 𝑎< e
Bx𝑎> e2
Cx𝑎> e
Dx𝑎> 2e
5x'2024·IJij·÷üýþ)·𝑥;#$%(e−1)(ln𝑥+ 𝑎𝑥) ≥𝑥e𝑎𝑥−1𝑥∈1
2 ,1 ¤:!MAª¬
𝑎;Ā
12J' )
Ax(0,2 + 2ln2]
Bx 1
e ,e
Cx(0,4]
Dx 1
2e ,e
6x'2024·IJij·÷üýþ)ÿt8
𝑓(𝑥) =
1−eln𝑥−3
𝑥
,𝑥> 0
(𝑥−2)e𝑥−2e𝑥
𝑥,𝑥< 0
M#$%𝑓(𝑥) >
𝑎
𝑥&*+MA¬
𝑎;Ā
12d' )
Ax(−∞,3)
Bx(6e−2, + ∞)
Cx(6e−2,3)
Dx(−∞,6e−2)
7x'2024·»Ŭ·÷üýþ)ÿt8
𝑓(𝑥) =
ln𝑥
𝑥,𝑔(𝑥) = 𝑎𝑥e−𝑎𝑥Mġ𝑥1 ∈(0,1),𝑥2 ∈(−∞,0)Â𝑓(𝑥1) = 𝑔
(𝑥2)MA¬
𝑎;Ā12d' )
Ax(−∞,−2)
Bx(−2,−1)
Cx(−1, + ∞)
Dx(0, + ∞)
8x'2023·Īŭ=·a÷)ġ¬
𝑎, 𝑏MĈU¬
𝑥∈[0,1]MÂ#$%𝑥3 −𝑚≤𝑎𝑥+ 𝑏≤𝑥3 +𝑚&*
+MA¬
m ;Ā12J' )
Ax
3
9 , + ∞
Bx 8 3
9 , + ∞
Cx
3
3 , + ∞
Dx
3
2 , + ∞
öEë
9x'2024·Ů·a÷)Ğ𝑓(𝑥) = (1 + 𝑥)ln𝑥,𝑔(𝑥) = (𝑎−1)𝑥M𝑓(𝑥) ≤𝑔(𝑥)𝑥∈[1,2]&*+MA¬
a
;¦ÀJ' )(Ś:ln2 ≈0.69)
Ax
3−ln2
2
Bx3
Cx2
Dx
2+3ln2
2
10x'2024·Ģďůć·÷üýþ)ÿt8
𝑓(𝑥) = 𝑥cos𝑥−sin𝑥MÄÅĽ5Pª«;J' )
Ax8
𝑓(𝑥)𝑥=
π
2nMĀÔė−1
Bx·∀𝑥∈[0,π]M𝑓(𝑥) ≤0&*+
Cx0 < 𝑥1 < 𝑥2 < πMA
𝑥1
𝑥2 <
sin𝑥1
sin𝑥2
Dx·∀𝑥∈0, π
2 M#$%𝑎<
sin𝑥
𝑥< 𝑏&*+MA𝑎;md
2
πM𝑏;ėd1
11x'2024·ĥŰ·÷üýþ)Ğ𝑥1,𝑥2(𝑥1 < 𝑥2)JĚ𝑦= 𝑎9ęĚ𝑓(𝑥) = 𝑥(1−ln𝑥);zZL;űŲųMA
' )
Ax𝑥1𝑥2 < e
Bx𝑥2ln𝑥1 > 𝑥1ln𝑥2
Cx∃𝑎∈(0,1),𝑥2−𝑥1 > e𝑎
Dx∀𝑎∈(0,1),𝑥1ln𝑥1 + 𝑥2 > 𝑎
ÝEŴŵ
12x'2024·āĂ*ă·Ý÷)#$%e𝑚𝑥(𝑚𝑥−ln2)−𝑥ln𝑥2 ≥0MĈU𝑥∈1
e , + ∞&*+MAª¬
𝑚;
Ā12J
.
13x'2024·đùŶŷ·Ý÷)𝑥𝑘−e𝑥
e𝑥
≥2(𝑘ln𝑥−𝑥)(𝑘> 0)ĈU;𝑥∈(0, + ∞)&*+MA k ;Ā12J
x
14x'2024·Ĺĥ·Ý÷)ÿt8
𝑓(𝑥) = (𝑥−2)e𝑥+ ln𝑥M𝑔(𝑥) = 𝑎𝑥+ 𝑏MĈU𝑎∈(−∞,1]Mġ𝑥∈(0,1)
Â#$%𝑓(𝑥) ≥𝑔(𝑥)*+MA²³;𝑏;mĿ
d
.
āE!ň
15x'2024·ĠùŸŹ·Ý÷)ÿt8
𝑓(𝑥) = 𝑥2−2𝑥+ 𝑎ln𝑥,(𝑎∈𝑅).
(1)458
;ĕĖ~
(2)ĈU;𝑥1,𝑥2 ∈(0, + ∞),𝑥1 ≠𝑥2MÂ
𝑥2𝑓(𝑥1)−𝑥1𝑓(𝑥2)
𝑥1−𝑥2
> 0&*+MA¬
𝑎;Ā12.
16x'2024·IJij·÷üýþ)ÿt8
𝑓(𝑥) = 𝑥2−2𝑎ln𝑥−2(𝑎∈R)x
(1)45𝑓(𝑥);ĕĖ~
(2)#$%𝑓(𝑥) ≤2(ln𝑥)2 + 𝑥2−2𝑥¹º(1, + ∞):!M0¬
a ;Ā12x
17x'2024·đĒźŻ·a÷)Ğ8
𝑓(𝑥) = e𝑥+𝑎sin𝑥M𝑥∈[0, + ∞).
(1)Ü𝑎= −1nM𝑓(𝑥) ≥𝑏𝑥+ 1[0, + ∞)&*+M0¬
𝑏;Ā12
(2)𝑎> 0,𝑓(𝑥)[0, + ∞)ġżLM0¬
𝑎;Ā12.
18x'2024·āĂČč·÷üýþ)ÿt8
𝑓(𝑥) = 𝑥2
2 −𝑥ln𝑥,𝑔(𝑥) = 𝑎(𝑥+ ln𝑥) + 𝑎2−
𝑎
2.
(1)0𝑓(𝑥)ŽžL;ěĚWX
(2)0<
ġ𝑎∈0, 1
2 MÂ𝑓(𝑥) ≥𝑔(𝑥)¹º(1, + ∞)¤&*+MÊ𝑓(𝑥) = 𝑔(𝑥)(1, + ∞)¤:!.
19x'2024·Ĝĝ·Ý÷)ÿt𝑓(𝑥) = (2𝑥−1)e𝑎𝑥−𝑥𝑥= 0¿;ěĚWXd𝑥+ 𝑦+ 𝑏= 0x
(1)0¬
𝑎,𝑏;
(2)<=
𝑓(𝑥)ſ:aÔL𝑥0MÊ𝑓(𝑥0) < −
3
4x
(3)𝑔(𝑥) = (𝑘𝑥−1)e𝑘𝑥−𝑥MJġ𝑘Â𝑔(𝑥) ≥−1&*+Mġƀ0g𝑘;Ā12M#ġƀƁ=Ƃx