Himpunan penyelesaian dari persamaan :
Cos2
+ 7sin – 4 = 0, untuk 0 ≤ x ≤ 360
A. {240, 300}
B. {210, 330}
C. {120, 240}
D. {60, 120}
E. {30, 150}
Cos2
A. {240, 300}
B. {210, 330}
C. {120, 240}
D. {60, 120}
E. {30, 150}
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* cos 2x = 1 - 2sin^2 x
1 - 2sin^2 x + 7 sinx - 4 = 0
-2sin^2 x + 7 sin x - 3 = 0 (x -1)
2sin^2 x - 7 sin x + 3 = 0
(2 sinx - 1)(sin x - 3) = 0
2 sinx - 1 = 0 atau sinx - 3 = 0
sinx = 1/2 sinx = 3 (TIDAK MEMENUHI)
sinx = sin 30
x = 30 + n.360 = 30
x = (180 - 30) + n.360 = 150
jawaban : D