hitung luas x dan besar sudut DBC

Bab Garis dan Sudut
Matematika SMP Kelas VII

A]
4x - 10° + 90° + 20° = 180°
4x = 180° - 100°
4x = 80°
x = 80° : 4
x = 20°

B] ∠DBC = 4x - 10°
∠DBC = 4 . 20° - 10°
∠DBC = 80°- 10°
∠DBC = 70°