Diketahui segitiga ABC dengan AB=20cm AC=30cm dan sudut b=140 derajat. Hitunglah panjang BC dan sudut A

B =140°
AC = b = 30 cm
AB = c = 20cm
Sudut A?

[tex] \frac{b}{sin \: b} = \frac{c}{sin \: c} \\ \frac{30cm}{sin \: 140} = \frac{20cm}{sin \: c} \\ sin \: c \: \times 30cm \: = 20cm \: \times sin140 \\ sin \: c = \frac{20cm \times 0.642787}{30cm} \\ sin \: c = 0.428524 \\ sudut \: c = 25.37[/tex]
Sudut A = 180° - sudut B - sudut C
= 180° - 140° - 25,37°
= 14,63°

BC = a

[tex] \frac{a}{sin \: a} = \frac{b}{sinb} \\ \frac{a}{sin14.63} = \frac{30cm}{sin140} \\ a\times \: sin \: 140 \: = 30cm \times sin \: 14.63 \\ \\ a = \frac{30cm \times0.252576 }{0.642787} \\ = 11.788cm[/tex]