Geometry Practice Test 2

In ΔBOC,
∠1 + ∠2 = 180 - 65
∠1 + ∠2 = 115° ......(i)
In ΔABC,
∠A + ∠ABC + ∠BCA = 180°
∠A + (180 - 2∠1) + (180 - 2∠2) = 180°
∠A + 360° - 2 (∠1 + ∠2) = 180°
∠A + 360° - 2(115°) = 180° [using eq. (i)]
∠A + 360° - 230° = 180°
∠A = 180 + 230 - 360
∠A = 50°