Chapter 6: Lines and Angles

Q1. If two angles of a triangle are 60° and 80°, find the third angle.

Solution

Third angle = 180° - 60° - 80° = 40°

Q2. Prove that vertically opposite angles are equal.

Solution

Let lines AB and CD intersect at O.
∠AOC + ∠COB = 180° (linear pair)
∠BOD + ∠COB = 180° (linear pair)
∠AOC = ∠BOD ✓