Question

Answer this question plz its urgent....

Answer 1

Given quadrilateral is a cyclic quadrilateral.
So opposite angles are supplementary.   ∠ A + ∠C = 180°
      => ∠C = 180- 60 = 120°

Chord BD makes an angle ∠A = 60° at the circle at A. So chord BD makes an angle of 2*60° =120° at the center O.

      => ∠DOB = 120°

In ΔOBD:  ∠ ODB + ∠OBD = 180 - ∠DOB = 60°
  
In ΔCDB:   ∠CDB + ∠CBD = 180° - ∠C = 60°

Hence LHS = RHS. Proved.