YZAB is a quadrilateral and OYBA is a trapezium in which OY // BA and ∠ZYB = 111°, ∠YBA = 120°, ∠ZAB = 68° and BA = BY. Find
- ∠YZO
- ∠BYO
- ∠YAB.
(a)
∠YZO
= 360° - 120° -111° - 68°
= 61° (Sum of angles in a quadrilateral)
(b)
∠BYO
= 180° - 120°
= 60° (Interior angles, YO//BC)
(c)
∠YAB
= (180° - 120°) ÷ 2
= 60 ÷ 2
= 30° (Isosceles triangle)
Answer(s): (a) 61°; (b) 60°; (c) 30°