Phương trình lưꢀng giác
Gv:Lê Quꢁc Huy
2
Phương trình lưꢀng giác
ðS: x = + , x = + kπ, x = +
3
Gv:Lê Quꢁc Huy
19
2
2
.10. 3sin x +cos2x−2 = 0
π
kπ
2
π
π
kπ
III.
PHƯƠNG TRÌNH dꢋng: asinu+bcosu = c
4
2
6
2
2
2
hoꢒc asinu+bcosu = csinv hoꢒc asinu+bcosu = c cosv
F6. sin x +sin 3x−3cos 2x = 0
2
2
2
2
hoꢒc asinu+bcosu = csinv +d cosv vꢎi a + b = c + d
ðH Tài Chính Kꢇ Toán 01
2
2
Cách giꢂi: Chia 2 vꢇ cho a + b
.
π
1
2
5 −1
2
ðS: x = ± +kπ, x = ± arccos
+kπ
kπ
3
.1. sin x − 3 cos x = 2 ; 3.2 . cos2x − 3 sin2x = 3 .
3
2
3
.3. sin2x
.5. 3sin x
−
3 cos2x
4cos x
=
2
;
3.4. sin3x + 3 cos3x = − 3
.
2
2
2
F7. sin x +sin 3x = cos 2x +cos 4x
ðH Kinh Tꢇ Quꢀc Dân ðS: x = + , x =
3
−
=
5
;
3.6. 4sin x
−
3cos x
=
5
.
π
kπ
π
+
π
π
3
.7. sin(x
.8. sin(x
+
)
−
3 cos(x
3 cos(x
+
)
=
2
.
4
2
10
5
3
3
2
21π
2
2
π
π
F8. sin 4x −cos 6x = sin
+10x
3
+
)
−
+
)
=
2sin108x
.
3
3
π
π
kπ
+
3
3
3
.9.sin2x − 3 cos2x = 2cos3x . 3.10. sin5x − 3 cos5x + 2sin x = 0
.11. 2sin3x−sin2x + 3cos2x = 0
.12. 2sin x(cos x−1) = 3cos2x
.
ðH Dưꢓc Hà Nꢔi 99
ðS x = +kπ, x =
2
20 10
.
2
2
2
2
F9. sin 3x−cos 4x = sin 5x−cos 6x
ðH 02 KHꢀi B
.
kπ kπ
2
2sin2x +1
ðS: x =
, x =
3
3
3
3
.13. cos7x cos5x − 3 sin2x =1−sin7x.sin5x
.14. 3sin x− 3cos3x = 4sin x−1
.15.3sin3x− 3cos9x =1+4sin 3x
.16. 3sin4x−cos4x = sin x− 3 cos x
.
9
3
2
2
2
.
F10. 2cos x +2cos 2x +2coss 3x−3= cos4x
ðH SP TPHCM 2000
(
)
3
.
π
kπ
4
ðS: x = +
.
8
2
2
2
2
2
2
2
IV.PHƯƠNG TRÌNH dꢋng:
F11. sin x +sin 2x +sin 3x = cos x +cos 2x +cos 3x +cos 4x
CðSP Thái Bình 99 Khꢀi A
2
2
asin x +bsin x cos x +ccos x +d = 0
hoꢒc asin x +bsin x cos x +csin x cos x + d cos x = 0
Cách giꢂi: Xét 2 trưꢅng hꢓp:
3
2
2
3
π
kπ
4
π
kπ
2
π
ðS: x = + , x = + , x = +kπ
8
4
2
2
4
4
TH1: cos x = 0 : Ta có sin x =1. Thay vào phương trình.
TH2: cos x ≠ 0 : Chia 2 vꢇ cho cos x hoꢒc cos x
F12. 3sin x +5cos x−3 = 0
ðH AN ND 01
2
3
π
π
ðS : x = +kπ, x = ± +kπ
2
.1. 8sin x + 3sin x.cos x +11cos x = 8
2
4
4
4
4
4
.
.2. −5sin x + 3sin x.cos x −cos2x = −4
2
6
2
4
4
)
.
F13. 4 sin x +cos x + 3sin4x = 2
(
2
.3. −5sin x +sin x.cos x − 2cos x = −3
2
.
π
kπ
π
+
12
kπ
2
2
2
.4. 2sin x +3sin 2x −10cos x = −1
ðH SP TPHCM 01
ðS: x = + , x = −
.
4
2
2
.5. 2sin x +sin 2x + cos2x = 0
.
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Mobile: 09748.77148