Mô tả:
200 CÂU GIẢI PHƯƠNG TRÌNH LƯỢNG GIÁC
........
Các dạng bài tập lượng giác
a/kiÕn thøc cÇn nhí vµ ph©n lo¹i bµi to¸n
d¹ng 1 Ph¬ng tr×nh bËc nhÊt vµ bËc hai , bËc cao víi 1 hµm sè lîng gi¸c
§Æt HSLG theo t víi sinx , cosx cã ®iÒu kiÖn t �1
Gi¶i ph¬ng tr×nh ……….theo t
NhËn t tho¶ m·n ®iÒu kiÖn gi¶i Pt lîng gi¸c c¬ b¶n
Gi¶i ph¬ng tr×nh:
2cos2x- 4cosx=1
�
1/ �
2/ 4sin3x+3 2 sin2x=8sinx
sinx
�
0
�
1-5sinx+2cosx=0
�
3/ 4cosx.cos2x +1=0
4/ �
� cos x �0
5/ Cho 3sin3x-3cos2x+4sinx-cos2x+2=0 (1) vµ cos2x+3cosx(sin2x-8sinx)=0 (2).
1
T×m n0 cña (1) ®ång thêi lµ n0 cña (2) ( nghiÖm chung sinx= )
3
3
4
6/ sin3x+2cos2x-2=0
7/ a/ tanx+
-2 = 0
b/
+tanx=7
cot x
cos 2 x
c* / sin6x+cos4x=cos2x
5
7
8/sin( 2 x
)-3cos( x
)=1+2sinx
9/ sin 2 x 2sin x 2 2sin x 1
2
2
10/ cos2x+5sinx+2=0 11/ tanx+cotx=4
13/ sin x 1 cos x 0
2
4
15/ 4sin 2 x 6sin x 9 3cos 2 x 0
cos x
d¹ng 2:
12/
14/ cos2x+3cosx+2=0
b
a 2 b2
� a b sin( x ) c
2
C¸ch 3: §Æt
§¨c biÖt :
16/ 2cosx- sin x =1
Ph¬ng tr×nh bËc nhÊt ®èi víi sinx vµ cosx : asinx+bcosx=c
C¸ch 1: asinx+bcosx=c
a
§Æt cosx= 2
; sinx=
a b2
2
sin 2 2 x 4 cos 4 2 x 1
0
2sin x cos x
t tan
C¸ch : 2
b
�
�
a�
sin x cos x � c
a
�
�
b
tan � a sin x cos x.tan c
a
c
� sin( x ) cos
a
§Æt
2
x
ta cã sin x 2t 2 ;cos x 1 t 2 � (b c)t 2 2at b c 0
2
1 t
1 t
sin x 3 cos x 2sin( x ) 2 cos( x )
3
6
2.
sin x �cos x 2 sin( x � ) 2 cos( x m )
4
4
3.
sin x 3 cos x 2sin( x ) 2 cos( x )
3
6
2
2
2
§iÒu kiÖn Pt cã nghiÖm :
a b �c
1.
gi¶i ph¬ng tr×nh :
1/ 2sin15x+ 3 cos5x+sin5x=k
2/ a : 3 sin x cos x
c:
3/
1
cos x
3 sin x cos x 3
víi k=0
b: 4sin x 3cos x
1
3 sin x cos x 1
cos 7 x 3 sin 7 x 2 0
Chuyªn ®Ò ph¬ng trinh lîng gi¸c
víi k=0 vµ k=4
6
6
4sin x 3cos x 1
*t×m nghiÖm x �(
2 6
; )
5 7
1
........
4/( cos2x- 3 sin2x)6/
3 sinx-cosx+4=0
5/
cos x 2sin x.cos x
3
2 cos 2 x sin x 1
1 cos x cos 2 x cos 3x 2
(3 3 sin x)
2 cos 2 x cos x 1
3
D¹ng 3 Ph¬ng tr×nh ®¼ng cÊp ®èi víi sin x vµ cosx
§¼ng cÊp bËc 2: asin2x+bsinx.cosx+c cos2x=0
C¸ch 1: Thö víi cosx=0 Víi cosx �0 .Chia 2 vÕ cho cos2x ta ®îc:
atan2x+btanx +c=d(tan2x+1)
C¸ch2: ¸p dông c«ng thøc h¹ bËc
§¼ng cÊp bËc 3: asin3x+b.cos3x+c(sinx+ cosx)=0 hoÆc
asin3x+b.cos3x+csin2xcosx+dsinxcos2x=0
XÐt cos3x=0 vµ cosx �0 Chia 2 vÕ cho cos2x ta ®îc Pt bËc 3 ®èi víi tanx
Gi¶i ph¬ng tr×nh
1/a/ 3sin2x- 3 sinxcosx+2cos2x cosx=2
b/ 4 sin2x+3 3 sinxcosx-2cos2x=4
c/3 sin2x+5 cos2x-2cos2x-4sin2x=0
d/ 2 sin2x+6sinxcosx+2(1+ 3 )cos2x-5- 3 =0
3
2/ sinx- 4sin x+cosx=0 2 c¸ch +/ (tanx -1)(3tan2x+2tanx+1)=0
x k
+ sin3x- sinx+ cosx- sinx=0 � (cosx- sinx)(2sinxcosx+2sin2x+1)=0
4
2
2
3/ tanx sin x-2sin x=3(cos2x+sinxcosx)
4/ 3cos4x-4sin2xcos2x+sin4x=0
5/ 4cos3x+2sin3x-3sinx=0
6/ 2 cos3x= sin3x
7/ cos3x- sin3x= cosx+ sinx
3
8/ sinx sin2x+ sin3x=6 cos x
9/sin3(x- /4)= 2 sinx
Dang 4 Ph¬ng tr×nh vÕ tr¸i ®èi xøng ®èi víi sinx vµ cosx
*
a(sin x+cosx)+bsinxcosx=c
®Æt t= sin x+cosx
t � 2
*
t 2 1 =c
� at + b
� bt2+2at-2c-b=0
2
a(sin x- cosx)+bsinxcosx=c
®Æt t= sin x- cosx
t � 2
1 t =c
� at + b
� bt2 -2at+2c-b=0
2
2
Gi¶i ph¬ng tr×nh
1
1
1
1/ a/1+tanx=2sinx +
b/ sin x+cosx=
cos x
tan x cot x
2/ sin3x+cos3x=2sinxcosx+sin x+cosx
3/ 1- sin3x+cos3x= sin2x
4/ 2sinx+cotx=2 sin2x+1
5/ 2 sin2x(sin x+cosx)=2
6/ (1+sin x)(1+cosx)=2
7/ 2 (sin x+cosx)=tanx+cotx
3
8/1+sin3 2x+cos32 x= sin 4x
9/* a* 3(cotx-cosx)-5(tanx-sin x)=2
2
9/b*: cos4x+sin4x-2(1-sin2xcos2x) sinxcosx-(sinx+cosx)=0
1
1
10
10/ sin x cos x 4sin 2 x 1
11/ cosx+
+sinx+
=
sin x 3
cos x
12/ sinxcosx+ sin x cos x =1
dang 5 Gi¶i ph¬ng tr×nh b»ng ph¬ng ph¸p h¹ bËc
C«ng thøc h¹ bËc 2
C«ng thøc h¹ bËc 3
1 cos 2 x
3cos x cos 3 x
3sin x sin 3 x
1 cos 2 x
cos2x=
; sin2x=
cos3x=
; sin3x=
2
4
2
4
Gi¶i ph¬ng tr×nh
1/ sin2 x+sin23x=cos22x+cos24x
2/ cos2x+cos22x+cos23x+cos24x=3/2
2
2
2
3/sin x+ sin 3x-3 cos 2x=0
5x
9x
4/ cos3x+ sin7x=2sin2(
)-2cos2
4 2
2
2
2
2
2
5/ sin 4 x+ sin 3x= cos 2x+ cos x víi x �(0; )
Chuyªn ®Ò ph¬ng trinh lîng gi¸c
2
........
6/sin24x-cos26x=sin( 10,5 10x ) víi x �(0; )
7/ cos4x-5sin4x=1
2
8/4sin3x-1=3- 3 cos3x
9/ sin22x+ sin24x= sin26x
10/ sin2x= cos22x+ cos23x
11/ (sin22x+cos42x-1): sin x cos x =0
k k �
2
2
2
;
12/ 4sin3xcos3x+4cos3x sin3x+3 3 cos4x=3 x �
�
� 13/ 2cos 2x+ cos2x=4 sin 2xcos x
2
�24 2 8
x
14/ cos4xsinx- sin22x=4sin2( )-7/2 víi
x 1 <3
4 2
15/ 2 cos32x-4cos3xcos3x+cos6x-4sin3xsin3x=0
16/ sin3xcos3x +cos3xsin3x=sin34x
17/ * 8cos3(x+ )=cos3x
3
18/cos10x+2cos24x+6cos3xcosx=cosx+8cosxcos23x
sin 5 x
19/
=1
5sin x
20 / cos7x+ sin22x= cos22x- cosx
21/ sin2x+ sin22x+ sin23x=3/2
22/ 3cos4x-2 cos23x=1
Dang 6 : Ph¬ng tr×nh LG gi¶i b»ng c¸c h»ng ®¼ng thøc
* a3 �b3=(a �b)(a2 mab+b2)
* a4- b4=( a2+ b2) ( a2- b2)
* a8+ b8=( a4+ b4)2-2 a4b4
* a6 �b6=( a2 �b2)( a4 ma 2b2+b4)
Gi¶i ph¬ng tr×nh
1/ sin4
x
x
+cos4 =1-2sinx
2
2
2/ cos3x-sin3x=cos2x-sin2x
3/ cos3x+ sin3x= cos2x
4/
sin 4 x cos4 x 1
(tan x cot x) v« nghiÖm
sin 2 x
2
7
6/sin4x+cos4x= cot( x ) cot( x)
8
3
6
13
cos22x
8
7/ cos6x+sin6x=2(cos8x+sin8x)
8/cos3x+sin3x=cosx-sinx
9/ cos6x+sin6x=cos4x
10/ sinx+sin2x+sin3x+sin4x= cosx+cos2x+cos3x+cos4x
x
x
1
11/ cos8x+sin8x=
12/ (sinx+3)sin4 -(sinx+3) sin2 +1=0
8
2
2
Dang 7 : Ph¬ng tr×nh LG biÕn ®æi vÒ tÝch b»ng 0
1/ cos2x- cos8x+ cos4x=1
2/sinx+2cosx+cos2x-2sinxcosx=0
3/sin2x-cos2x=3sinx+cosx-2 4/sin3 x+2cosx-2+sin2 x=0
5/ 3sinx+2cosx=2+3tanx
6/ 3 sin2x+ 2 cos2x+ 6 cosx=0
2
sin 3 x sin 5 x
7/ 2sin2x-cos2x=7sinx+2cosx-4
8/
3
5
5
1
9/ 2cos2x-8cosx+7=
10/ cos8x+sin8x=2(cos10x+sin10x)+ cos2x
cos x
4
11/ 1+ sinx+ cos3x= cosx+ sin2x+ cos2x
12/ 1+sinx+cosx+sin2x+cos2x=0
13/ sin2 x(tanx+1)=3sinx(cosx-sinx)+3
1
1
14/ 2sin3x=2cos3x+
15/cos3x+cos2x+2sinx-2=0
sin x
cos x
5/cos6x-sin6x=
16/cos2x-2cos3x+sinx=0
17/ tanx–sin2x-cos2x+2(2cosx-
18/sin2x=1+ 2 cosx+cos2x
20/ 2tanx+cot2x=2sin2x+
22/ 1+tanx=sinx+cosx
24/ 2 2 sin( x
19/1+cot2x=
1
sin 2x
1
1
)=
4 sin x cos x
Chuyªn ®Ò ph¬ng trinh lîng gi¸c
1 cos 2 x
sin 2 2 x
1
)=0
cos x
21/cosx(cos4x+2)+ cos2x-cos3x=0
23/ (1-tanx)(1+sin2x)=1+tanx
25/ 2tanx+cotx= 3
2
sin 2x
3
........
26/ cotx-tanx=cosx+sinx
27/ 9sinx+6cosx-3sin2x+cos2x=8
Dang 8 : Ph¬ng tr×nh LG ph¶i thùc hiÖn c«ng thóc nh©n ®«i, h¹ bËc
cos2x= cos2x- sin2x =2cos2x-1=1-2sin2x
2t
1 t2
sin2x=2sinxcosx
sinx =
;
cosx=
1 t2
1 t2
2 tan x
tan2x=
1 tan 2 x
Gi¶i ph¬ng tr×nh
1
1/ sin3xcosx= + cos3xsinx
2/ cosxcos2xcos4xcos8x=1/16
4
3/tanx+2cot2x=sin2x
4/sin2x(cotx+tan2x)=4cos2x
5/ sin4x=tanx
6/ sin2x+2tanx=3
7/ sin2x+cos2x+tanx=2
8/tanx+2cot2x=sin2x
9/ cotx=tanx+2cot2x
3
10/a* tan2x+sin2x= cotx
b* (1+sinx)2= cosx
2
Dang 9 : Ph¬ng tr×nh LG ph¶i thùc hiÖn phÐp biÕn ®æi tæng_tÝch vµ tÝch_tæng
Gi¶i ph¬ng tr×nh
1/ sin8x+ cos4x=1+2sin2xcos6x
2/cosx+cos2x+cos3x+cos4x=0
sin 3 x sin x
sin 2 x cos 2 x t×m x � 0; 2 4/ sinx+sin2x+sin3x+sin4x=0
3/
1 cos 2 x
5/ sin5x+ sinx+2sin2x=1
6/
3 cos 2 x cot 2 x
cot 2 x cos 2 x
tanx=
�
� �
�
4sin � x �
cos � x �
4
4
�
� �
�
7/ tanx+ tan2x= tan3x
8/ 3cosx+cos2x- cos3x+1=2sinxsin2x
Dang 10 : Ph¬ng tr×nh LG ph¶i ®Æt Èn phô gãc A hoÆc ®Æt hµm B
Gi¶i ph¬ng tr×nh
3 x 1
3x x �3 k 2 ; 4 k 2 ; 14 k 2 �
1/ sin(
) �
)=sin2x sin( x )
� 2/ sin( 3 x
)= sin(
15
15
�5
10 2 2
10 2
4
4
3
x
3/(cos4x/3 – cos2x): 1 tan 2 x =0 x k 3
4/ cosx-2sin(
)=3 x k 4
2 2
7
k �
� k ;
5/ cos( 2 x
)=sin(4x+3 ) x �
6/3cot2x+2 2 sin2x=(2+3 2 )cosx
�
�
2
�6
2
7/2cot2x+
2
+5tanx+5cotx+4=0
cos 2 x
x
k
4
8/ cos2x+
1
1
=cosx+
cos 2 x
cos x
1 sin 2 x 1 tan x
1
1
7
�
k 2 �11/
+2 2 =5 x �
+2
=3
� k 2 ; k 2 ;
6
6
�2
sin x
sin x
1 sin 2 x 1 tan x
Dang 11 : Ph¬ng tr×nh LG ph¶i thùc hiÖn c¸c phÐp biÕn ®æi phøc t¹p
9/sinx- cos2x+
Gi¶i ph¬ng tr×nh
1/ 3 4 6 (16 3 8 2) cos x 4 cos x 3
3/ 5cos x cos 2 x +2sinx=0 x 6 k 2
2 sin x tan x
2
5/
2 cos x 2 x � 3 k 2
tan x sin x
7/tan2xtan23 xtan24x= tan2x-tan23 x+tan4x
9/sin3x=cosxcos2x(tan2x+tan2x)
�
�4
�
�
x � k 2
4
�
x
k
4
2
�
�
x�
� k 2 ; � k 2 �
4
�3
x k
x k ; k , tan 2
�
2/cos � 3 x 9 x 2 16 x 80 �=1 t×m n0 x�Z x 21; 3
�4
�
4/3cotx- tanx(3-8cos2x)=0
x � k
3
6/sin3x+cos3x+ sin3xcotx+cos3xtanx= 2sin 2x
x
k
4
�
tan 2 x �
� 4
�
�
x
2
�
�
x
k 2
4
k
�
8/tanx+tan2x=-sin3xcos2x x �
� k 2 �
�3
10/
x k
11/cos2 � sin x 2 cos 2 x �-1=tan2 �
�x
x
sin x sin x 1 sin 2 x cos x
x k ;sin x
5 1
2
k 2
4
x �
�x
�3x �
� 6 sin � � 2sin �
� 2sin � �
�5 12 �
�5 12 �
�5 3 �
�5 6 �
12/ 2 cos �
�
2t
1 t2
5
5
� 5
�
x�
k 5 ;
k 5 ;
k 5 �
3
4
� 12
Dang 12 : Ph¬ng tr×nh LG kh«ng mÉu mùc, ®¸nh gi¸ 2 vÕ ,tæng 2 lîng kh«ng ©m,vÏ 2 ®å thÞ b»ng ®¹o hµm
Gi¶i ph¬ng tr×nh
1/ cos3x+ 2 cos 2 3x =2(1+sin22x) x k
2/ 2cosx+ 2 sin10x=3 2 +2sinxcos28x x 4 k
3/ cos24x+cos26x=sin212x+sin216x+2 víi x � 0;
Chuyªn ®Ò ph¬ng trinh lîng gi¸c
2
�
� k 2 �
4/ 8cos4xcos22x+ 1 cos 3x +1=0 x �
�
� 3
4
........
5/ sin
x
cos x
x0
8/( cos2x-cos4x)2=6+2sin3x
Chuyªn ®Ò ph¬ng trinh lîng gi¸c
6/ 5-4sin2x-8cos2x/2 =3k t×m k �Z* ®Ó hÖ cã nghiÖm
x
k
2
9/
1
1 cos x 1 cos x cos 2 x sin 4 x
2
2
7/ 1- x =cosx
2
x � k 2
4
5
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