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Truy cp ti t?i liu hc tp, b?i ging min ph?
C?u 3: Gii c?c phng tr?nh sau:
1).
2
cos
2x
6
4
sin
x
cos
x
1
0
2).
4
sin
x
4
2
cos
x
4
3
2 0
3).
8
sin
x
sin
2x
6
sin
x
4
cos
4
2x
5 7 cos x
4). 2
3
sin
x
8
cos
x
8
2
cos2
x
8
3 1
5).
1 cos x cos 2x cos 3x 2
2 cos2 x cos x 1
3
3
3 sin x
6). 8 sin x 3 1 cos x sin x
7). 2cos3 x 2sin3 x 2sin2 xcos x 2cos2 xsin x 2 0
8). 5cos x sin x sin 3x cos 3x 2 2 2 sin 2x
LI GII
1).
2
cos
2x
6
4
sin
x
cos
x
1
0
2
cos
2x cos
6
sin 2x sin
6
2
sin
2x
1
0
3 cos 2x sin 2x 1
3 cos 2x 1 sin 2x 1 cos 2x cos sin 2x sin 1
2
2
2
6
62
cos
2x
6
cos
3
2x 2x
6 6
3
3
k2 k2
x x
4
k k 12
,
k
Vy nghim ca phng tr?nh: x k,x k,k
4
12
2).
4
sin
x
4
2
cos
x
4
3
2 0
4. sin x cos x 2. sin x cos x 3 2
2
2
sin x cos x 1
2
sin
x
4
1
sin
x
4
1 2
x x
4 4
4
k2 k2 4
x x
k2 k2 2
Vy nghim ca phng tr?nh: x k2,x k2,k
2
3).
8
sin
x
sin
2x
6
sin
x
4
cos
4
2x
5 7 cos x
4
cos
x
cos
3x
3
sin
3x
sin
2
x
5
7
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?
4cos x cos 3x 3sin 3x cos x 5 7 cos x 3sin 3x 4cos 3x 5
3 sin 3x 4 cos 3x 1 sin 3x.cos cos 3x.sin 1 sin 3x 1
5
5
3x k2 x k2 . (Vi 3 cos , 4 sin )
2
36 3
5
5
Vy nghim ca phng tr?nh: x k2 36 3
4). 2
3
sin
x
8
cos
x
8
2
sin2
x
8
3 1
?p
dng
c?ng
thc
nh?n
?i:
2
sin
x
8
cos
x
8
sin
2x
4
,
v?
h
bc
2
sin2
x
8
1
cos
2x
4
ta c:
3
sin
2x
4
1
cos
2x
4
3 1
3
sin
2x
4
cos
2x
4
3
3 2
sin
2x
4
1 2
cos
2x
4
3 2
sin
2x
4
cos
6
cos
2x
4
sin
6
3 2
sin
2x
4
6
sin
3
2x 2x
4 4
6 6
3
k2 k2 3
x x
3 k 8 13 k 24
Vy nghim ca phng tr?nh: x 3 k,x 13 k,k
8
24
5).
1 cos x cos 2x cos 3x 2
2 cos2 x cos x 1
3
3
3 sin x
* . iu kin 2cos2 x cos x 1 0
1 cos 2x cos 3x cos x 2 3 3 sin x
2 cos2 x 1 cos x
3
2 cos2 x 2 cos 2x.cos x 2 3 3 sin x
cos 2x cos x
3
2 cos xcos 2x cos x 2 3 3 sin x
cos 2x cos x
3
2 cos x 2 3 3 sin x 3 cos x sin x 3 3
3 cos x 1 sin x 3 cos x.cos sin x sin 3
2
2
2
6
62
cos
x
6
cos
6
x x
6 6
k2 6 k2
6
x x
k2 3 k2
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?
Thay hai h nghim ca x v?o iu kin ta thy tha.
Vy nghim ca phng tr?nh: x k2 , x k2 . 3
6).
8 sin x
3 cos x
1 sin x
.
iu
kin
sin x 0 cos x 0
Quy ng mu c: 8sin2 xcos x 3 sin x cos x
H bc sin2 x c: 41 cos 2xcos x 3 sin x cos x
4cos x 4cos 2xcos x 3 sin x cos x
4cos x 2cos x cos 3x 3 sin x cos x
cos x 3 sin x 2cos 3x 1 cos x 3 sin x cos 3x
2
2
cos x.cos sin x.sin cos 3x
3
3
cos
x
3
cos
3x
3x 3x
x
k2 3
x
3
k2
x x
6
k k 12 2
So vi iu kin nghim ca phng tr?nh: x k , x k .
6
12 2
7). 2cos3 x 2sin3 x 2sin2 xcos x 2cos2 xsin x 2 0
2cos x sin x sin2 x sin xcos x cos2 x 2sin xcos x sin x cos x 2 0
2cos x sin x1 sin xcos x 2sin xcos xsin x cos x 2 0
2cos x sin x
2 2
2
cos
x
4
2
cos
x
4
1 2
cos
x
4
cos
3
x
4
3
k2
x
7 12
k2
x
4
3
k2
x
12
k2
So vi iu kin nghim ca phng tr?nh: x 7 k2,x k2,k
12
12
8). 5cos x sin x sin 3x cos 3x 2 2 2 sin 2x
5cos x sin x 3sin x 4sin3 x 4cos3 x 3cos x 2 2 2 sin 2x
8cos x sin x 4 sin3 x cos3 x 2 2 2 sin 2x
8cos x sin x 4sin x cos x1 sin xcos x 2 2 2 sin 2x
4sin x cos x2 1 sin xcos x 2 2 2 sin 2x
4
sin
x
cos
x
1
1 2
sin
2x
2
2 2 sin 2x
2sin x cos x2 sin 2x 2 2 2 sin 2x
sin x cos x 2 ( v? 2 sin 2x 0 ).
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?
2
sin
x
4
2
sin
x
4
1
x
4
2
k2
x
4
k2
Truy cp ti t?i liu hc tp, b?i ging min ph?
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