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Kelas 7 Matematika
Bab Bangun Datar

∠BAD = ∠BCD = 36°

CD = CB, maka ∠CDB = ∠CBD

∠CDB + ∠CBD + ∠BCD = 180°
2 . ∠CDB + 36° = 180°
2 . ∠CDB = 180° - 36°
∠CDB = 144°/2
∠CDB = 72°

∠ADC = 180° - ∠BAD
∠ADC = 180° - 36°
∠ADC = 144°

∠BDA = ∠ADC - ∠CDB
∠BDA = 144° - 72°
∠BDA = 72°