Tentukan penyelesaian persamaan trigonometri cos 2x=-1/2 untuk 0°≤x≤360°

cos2x = -1/2
cos2x = cos120
2x = 120 + 380k
x = 60 + 180k
k = 0 → x = 60°
k = 1 → x = 240°
2x = -120 + 360k
x = -60 + 180k
k = 1 → x = 120°
k = 2 → x = 300°
hp = {60°, 120°, 240°, 300°}

Ingat rumus:
cos x = cos α
x = α + 360k ATAU x = -α + 360k

Jwb:
cos 2x = -1/2
cos 2x = cos120
2x = 120 + 360k -------->> (sama" dibagi 2)
x = 60 + 180k

Untuk k = 0:
x = 60 + 180k
x = 60 + 180(0)
x = 60 + 0
x = 60°


Untuk k = 1:
x = 60 + 180k
x = 60 + 180(1)
x = 60 + 180
x = 240°

cos 2x = -1/2
cos 2x = 120
2x = -120 + 360k -------->> (sama" dibagi 2)
x = -60 + 180k

Untuk k = 1
x = -60 + 180k
x = -60 + 180(1)
x = -60 + 180
x = 120°

Untuk k = 2
x = -60 + 180k
x = -60 + 180(2)
x = -60 + 360
x = 300°

Hp = {60°, 120°, 240°, 300°}