Question
In figure, ∠X = 62°, ∠XYZ = 54°. If YO and ZO are the bisectors of ∠XYZ and ∠XZY respectively of ∆XYZ, find ∠OZY and ∠YOZ.

Solution
In ∆XYZ,
∠XYZ + ∠YZX + ∠ZXY = 180°
| ∵ The sum of all the angles of a triangle is 180°
⇒ 54° + ∠YZX + 62° = 180°
⇒ 116° + ∠YZX = 180°
⇒ ∠YZX = 180° - 116° = 64° ...(1)
∵ YO is the bisector of ∠XYZ

∵ ZO is the bisector of ∠YZX

| Using (1)
In ∆OYZ,
∠OYZ + ∠OZY + ∠YOZ = 180°
|∵ The sum of all the angles of a triangle is 180°
⇒ 27° + 32° + ∠YOZ = 180°
| Using (2) and (3)
⇒ 59° + ∠YOZ = 180°
⇒ ∠YOZ = 180° - 59° = 121°.