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Truy cp ti t?i liu hc tp, b?i ging min ph?
C?u 4: Gii c?c phng tr?nh lng gi?c sau:
1). sin4 cos4 x 2 sin 2x 3 sin2 2x 0 4
2). cos6 2x sin6 2x 15 cos 4x 1
8
2
3). sin4 x 5 cos4 x 1 3
4).
sin4
x cos4
x
cos
x
4
sin
x
3
4
1 2
5).
sin4 x cos 2x 4sin6 x 0
6). cos8x sin3 xcos x cos3 xsin x 1 0
LI GII
1). sin4 cos4 x 2 sin 2x 3 sin2 2x 0 1
4
1
1 2
sin2
2x
2
sin
2x
3 sin2 4
2x
0
1 sin2 2x 2 sin 2x 1 0 4
1'
t sin 2x t,t [1;1] . Phng tr?nh (1') tr th?nh: 1 t2 2t 1 0 4
t 4 2 3 t 4 2 3 . So vi iu kin nhn t 4 2 3 sin 2x 4 2 3
2x arcsin 4 2 3 2x arcsin 4 2
k2
x
3 k2
x
arcsin 4 2 3 2
arcsin 4 2 2
k,k
3
k,k
arcsin 4 2 3
arcsin 4 2 3
Vy nghim ca phng tr?nh: x
k, x
k,k .
2
2
2). cos6 2x sin6 2x 15 cos 4x 1 1
8
2
1 1 3 sin2 2x 15 cos 4x 1 1 3 1 cos 4x 15 cos 4x 1
4
8
2
42
8
2
8 31 cos 4x 15cos 4x 4 cos 4x 3
4
4x arccos 3 k2 x 1 arccos 3 k k
4
4
42
Vy nghim ca phng tr?nh: x 1 arccos 3 k k .
4
42
3). sin4 x 5 cos4 x 1 sin2 x 2 5 cos2 x 2 1
3
3
1 cos 2x 2
2
5 1 cos 2x
3
2
2
1
1 . t cos 2x t,t [1;1]
1 1 2t t2 5 1 2t t2 1 8t2 4t 4 0 t 1 t 1 .
4
34
2
Vi t 1 cos 2x 1 2x k2 x k,k
2
Vi
t
1
cos 2x
1
2x
3
k2
x
6
k
,k
2
2
2x
3
k2
x
6
k
Vy nghim ca phng tr?nh: x k, x k,x k,k
2
6
6
Truy cp ti t?i liu hc tp, b?i ging min ph?
Truy cp ti t?i liu hc tp, b?i ging min ph?
4).
sin4
x
cos4
x
cos
x
4
sin
x
3 4
1 2
1
1 2
sin2
2x
1 2
sin
2
sin
2x
1 2
1
1 2
sin2
2x
1 2
1
sin
2x
1 2
sin2 2x sin 2x 0 sin 2x 0 sin 2x 1
Vi sin 2x 0 2x k x k ,k
2
Vi sin 2x 1 2x k2 x k,k .
2
4
Vy nghim ca phng tr?nh: x k , x k,k
2
4
5). sin4 x cos 2x 4sin6 x 0 sin2 x 2 cos 2x 4 sin2 x 3 0
1
cos 2
2x
2
cos
2x
4
1
cos 2
2x
3
0
(1). t
cos 2x t,t [1;1] . Phng tr?nh (1) tr th?nh:
1 t 2
2
t
4
1
2
t
3
0
2t3
7t2
4t 3 0
t
3 (loi).
Kt lun phng tr?nh v? nghim.
6). cos 8x sin3 xcos x cos3 xsin x 1 0 1
1 cos 8x sin x cos x sin2 x cos2 x 1 0 cos 8x 1 sin 2x cos 2x 1 0 2
1 2 sin2 4x 1 sin 4x 1 0 2 sin2 4x 1 sin 4x 0 sin 4x 0 sin 4x 1
4
4
8
Vi sin 4x 0 4x k x k ,k .
4
Vi
sin 4x
1 8
4x 4x
arcsin
1 8
k2
arcsin
1 8
k2
x x
1 4
arcsin
1 8
k 2
4
1 4
arcsin
1 8
,k
k 2
Vy
nghim
ca
phng
tr?nh:
x
k , 4
x
1 4
arcsin
1 8
k , 2
x
4
1 4
arcsin
1 8
k ,k
2
C?u 5: Gii c?c phng tr?nh lng gi?c sau:
1).
sin 2x
3 cos 2x
2
2
cos
2x
6
2).
cot
x
1
tan x tan
x 2
sin
x
4
3). cot x tan x 2 4 sin 2x sin 2x
4).
2
2
sin
x
1
4
sin
x
1
cos
2x
4
sin
2x
4
5). cot x 1 cos 2x sin2 x 1 sin 2x ( H khi A 2003)
1 tan x
2
6). 5sin x 2 31 sin x tan2 x (H khi B 2004)
Truy cp ti t?i liu hc tp, b?i ging min ph?
Truy cp ti t?i liu hc tp, b?i ging min ph?
7). cos2 3xcos 2x cos2 x 0 (H khi A 2005).
8).
sin4
x
cos4
x
cos
x
4
sin
3x
4
3 2
= 0
(H khi D 2005).
9).
1
sin
x
cos
2x
sin
x
4
1 cos x (H khi A 2010).
1 tan x
2
10). sin4 x cos4 x 1 cot 2x 1 (1) [D b 2 H02]
5sin 2x
2
8 sin 2x
11). cot x tan x 4 sin 2x 2 .[H B03] sin 2x
12). 3cos 4x 8cos6 x 2cos2 x 3 0 (1) [D b 1 H B03]
13). cot x tan x 2 cos 4x [D b 2 H D03] sin 2x
LI GII
1).
sin 2x
3 cos 2x
2
2
cos
2x
6
1
1
4
1 2
sin
2x
3 2
2 cos 2x
2
cos
2x
6
4
cos
2x
cos
6
sin 2x sin
2
6
2
cos
2x
6
2 cos2
2x
6
cos
2x
6
0
cos
2x
6
0
cos
2x
6
1 2
Vi
cos 2x
6
0
2x
6
2
k
x
3
k 2
,k
Vi
cos
2x
6
1 2
2x 2x
6 6
k2
3
k2
3
x x
k
4
,k
k
12
Vy nghim ca phng tr?nh: x k , x k,x k,k
32
4
12
sin x 0
2).
cot
x
1
tan
x
tan
x 2
sin
x
4
1 .
iu
kin
cos x 0
cos
x
0
2
Ta
c?:
1 tan x tan x
1
sin x sin x 2
cos x cos x sin x sin x
2
2
cos
x
x 2
1
2
cos x cos x
cos x cos x
cos x cos x cos x
2
2
2
1 cos x sin x 4 cos2 x sin2 x 4sin xcos x 2sin 2x 1
sin x cos x
Truy cp ti t?i liu hc tp, b?i ging min ph?
Truy cp ti t?i liu hc tp, b?i ging min ph?
sin 2x
1
2x
6
k2
x
12
k
,
k
2
2x
5 6
k2
x
5 12
k
Vy nghim ca phng tr?nh: x k,x 5 k,k
12
12
3). cot x tan x 2 4 sin 2x sin 2x
1 .
iu
kin
sin 2x
0
x
k 2
1 cos x sin x 2 4 sin 2x cos2 x sin2 x 2 4 sin 2x
sin x cos x sin 2x
sin x cos x sin 2x
2 cos 2x 2 4 sin 2x sin 2x sin 2x
2cos 2x 2 4sin2 2x
cos 2x 1 2 1 cos2 2x
2cos2 2x cos 2x 1 0
cos 2x 1 cos 2x 1 . 2
Vi cos 2x 1 2x k2 x k,k (loi)
Vi
cos 2x
1
cos 2x
cos
2
2x
2 3
k2
x
3
k
,k
2
3
2x
2 3
k2
x
3
k
Vy nghim ca phng tr?nh: x k,x k,k
3
3
4).
2
2
sin
x
1
4
sin
x
1
cos
2x
4
sin
2x
4
1
2
2
sin
x
1
4
sin
x
1
cos
2x
4
sin
2x
4
2 2 sin x 1 4sin x 1
2
cos
2x
4
4
2 2sin x 1 4sin x 1 2 cos 2x
2 2sin x 1 4sin x 1 2 1 2sin2 x
2 2 sin2 x 2 2 2 sin x 4 0
sin x 1 sin x 2 (loi).
Vi sin x 1 x k2,k
2
Vi Vy nghim ca phng tr?nh: x k2,k
2
Truy cp ti t?i liu hc tp, b?i ging min ph?
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