Tolong ya saya lupa caranya....

X+75=2x x 2
X+75=4x
4x-x=75
3x=75
X=25

180-180-(x+75)
180-(25+75)
180-100
80

Kelas 8 Matematika
Bab Lingkaran

∠AOB = 2 . ∠ACB
x + 75° = 2 . 2x
75° = 4x - x
75° = 3x
x = 75°/3
x = 25°

∠OAB = ∠OBA (segitiga sama kaki)

∠OAB + ∠OBA + x + 75° = 180°
2 . ∠OAB = 180° - 100°
∠OAB = 80°/2
∠OAB = 40°