Perhatikan gambar berikut.
Pembahasan:
∠BAC + ∠ABC + ∠ACB = 180°
(2x + 2)° + (8x – 10°) + (3x – 7)° = 180°
(13x – 15)° = 180°
13x° = 180° + 15°
13x° = 195°
x° = 195°
13°
x° = 15°
∠ABC = (8x – 10)°
= (8 × 15 – 10)° = (120 – 10)° = 110°
∠CBD = 180° – ∠ABC = 180° – 110° = 70°