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Kelas 10 Matematika
Bab Trigonometri

∠C = 180° - 105° - 30°
∠C = 45°

BC/sin A = AB/sin C
BC/sin 30° = 5/sin 45°
BC = sin 30° . 5 / sin 45°
BC = (1/2) . 5 / (1/2 √2)
BC = 5/√2 . (√2)/(√2)
BC = (5/2) √2