Please bantu jawab☺️

Bagian A)
Cos x = 0
cos x = Cos 90 derajat
x1 = 90 + k × 360
k=0 -> 90 + 0 × 360 = 90
k=1 -> 90 + 1 × 360 = 450 (lebih dari 360)

x2 = -90 + k × 360
k=0 -> -90 + 0 × 360 = -90 (tdk ditulis ke hasil karena 90 = -90)
k=1 -> -90 + 1 × 360 = 270
k=2 -> -90 + 2 × 360 = 630 (lebih dari 360)

Hp = {90,270}

Bagian B)
Cos 2x = 1/2
cos 2x = Cos 60 derajat
2 x1 = 60 + k × 360
x1 = 30 + k × 180
k=0 -> 30 + 0 × 180 = 30
k=1 -> 30 + 1 × 180 = 210
k=2 -> 30 + 2 × 180 = 390 (lebih dari 360)
2 x2 = -120 + k × 360
x2 = -60 + k × 180
k=0 -> -60 + 0 × 180 = -60 (tdk ditulis ke hasil karena 60 = -60)
k=1 -> -60 + 1 × 180 = 60
k=2 -> -60 + 2 × 180 = 300

Hp = {30,60,210,300}