yang bisa pasti hebat banget

1. BC/sin A = AC/sin B
BC/sin 60° = 12/sin 45°
BC = 12.sin 60° / sin 45°
BC = 12(1/2√3)/1/2√2 = 6√3.2/√2 = 12√3/√2 = 6√6 cm

4. Pergunakan aturan kosinus,
AB² = AC² + BC² - 2AC.BC cos C
AB² = 12² + 4² - 2(12)(4) cos 30° = 144+16-96(1/2√3) = 160-48√3
AB = √(16(10-3√3)) = 4√(10-3√3)
Itu saja semoga membantu.