Geometry Practice Test 4

O is the orthocenter of ΔABC and ∠BAC = 80°
∠BAG = ∠CAG = 40°

In ΔAFB,
∠BAF +∠AFB+∠FBA = 180°
80° + 90° +∠FBA = 180°
∠FBA = 180° −170°
∠FBA = 10°
In ΔAOB,
∠OAB+∠ABO+∠AOB = 180°
10° + 40° +∠AOB = 180°
∠AOB = 180° − 50°
∠AOB = 130°
∠AOB+∠AOC+∠BOC = 360°
130° + 130° + ∠BOC = 360°
∠BOC = 360° − 260°
∠BOC = 100°