Geometry Practice Test 2

∠ACB + ∠ACD = 180° {linear pair}

∠ACD = 180° − 80°
∠ACD = 100°
∠CAD+∠CDA +∠ACD = 180°
{angle sum property}
x° + x° +100° = 180°
2x = 80° {∵AC = CD)
∠CAD = x = 40°
∠BAD−∠CAD = ∠BAC
∠BAC = 111° − 40° = 71°
In ΔABC,
∠BAC+∠B+∠BCA = 180°
71° + 80° +∠ABC = 180°
∠ABC = 29°